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CoffeeScript Logo
Try CoffeeScript Language Reference Integrations Resources GitHub
alert 'Hello CoffeeScript!'
alert('Hello CoffeeScript!');
Try CoffeeScript Introduction Overview CoffeeScript 2
What’s New in CoffeeScript 2 Compatibility
Installation Usage
Command Line Node.js Transpilation
Language Reference
Functions Strings Objects and Arrays Comments Lexical Scoping and Variable
Safety If, Else, Unless, and Conditional Assignment Splats, or Rest
Parameters/Spread Syntax Loops and Comprehensions Array Slicing and Splicing
Everything is an Expression Operators and Aliases Existential Operator
Destructuring Assignment Chaining Function Calls Bound (Fat Arrow) Functions
Generator Functions Async Functions Classes Prototypal Inheritance
Switch/When/Else Try/Catch/Finally Chained Comparisons Block Regular Expressions
Tagged Template Literals Modules Embedded JavaScript JSX
Type Annotations Literate CoffeeScript Source Maps Cake, and Cakefiles
"text/coffeescript" Script Tags Integrations
Build Tools Code Editors Frameworks Linters and Formatting Testing
Resources
Books Screencasts Examples Chat Annotated Source Contributing
GitHub Unsupported ECMAScript Features
let and const Named Functions and Function Declarations get and set Shorthand
Syntax
Breaking Changes From 1.x
Bound (Fat Arrow) Functions Default Values Bound Generator Functions Classes
super and this super and extends JSX and the < and > Operators Literate
CoffeeScript Parsing Argument Parsing and #! Lines
Changelog Browser-Based Tests Version 1.x Documentation
CoffeeScript Logo
CoffeeScript is a little language that compiles into JavaScript. Underneath that
awkward Java-esque patina, JavaScript has always had a gorgeous heart.
CoffeeScript is an attempt to expose the good parts of JavaScript in a simple
way.
The golden rule of CoffeeScript is: “It’s just JavaScript.” The code compiles
one-to-one into the equivalent JS, and there is no interpretation at runtime.
You can use any existing JavaScript library seamlessly from CoffeeScript (and
vice-versa). The compiled output is readable, pretty-printed, and tends to run
as fast or faster than the equivalent handwritten JavaScript.
Latest Version: 2.7.0
> # Install locally for a project:
> npm install --save-dev coffeescript
>
> # Install globally to execute .coffee files anywhere:
> npm install --global coffeescript
OVERVIEW
CoffeeScript on the topleft, compiled JavaScript output on the bottomright. The
CoffeeScript is editable!
# Assignment: number = 42 opposite = true # Conditions: number = -42 if opposite
# Functions: square = (x) -> x * x # Arrays: list = [1, 2, 3, 4, 5] # Objects:
math = root: Math.sqrt square: square cube: (x) -> x * square x # Splats: race =
(winner, runners...) -> print winner, runners # Existence: alert "I knew it!" if
elvis? # Array comprehensions: cubes = (math.cube num for num in list)
# Assignment:
number = 42
opposite = true
# Conditions:
number = -42 if opposite
# Functions:
square = (x) -> x * x
# Arrays:
list = [1, 2, 3, 4, 5]
# Objects:
math =
root: Math.sqrt
square: square
cube: (x) -> x * square x
# Splats:
race = (winner, runners...) ->
print winner, runners
# Existence:
alert "I knew it!" if elvis?
# Array comprehensions:
cubes = (math.cube num for num in list)
// Assignment: var cubes, list, math, num, number, opposite, race, square;
number = 42; opposite = true; if (opposite) { // Conditions: number = -42; } //
Functions: square = function(x) { return x * x; }; // Arrays: list = [1, 2, 3,
4, 5]; // Objects: math = { root: Math.sqrt, square: square, cube: function(x) {
return x * square(x); } }; // Splats: race = function(winner, ...runners) {
return print(winner, runners); }; if (typeof elvis !== "undefined" && elvis !==
null) { // Existence: alert("I knew it!"); } // Array comprehensions: cubes =
(function() { var i, len, results; results = []; for (i = 0, len = list.length;
i < len; i++) { num = list[i]; results.push(math.cube(num)); } return results;
})();
// Assignment:
var cubes, list, math, num, number, opposite, race, square;
number = 42;
opposite = true;
if (opposite) {
// Conditions:
number = -42;
}
// Functions:
square = function(x) {
return x * x;
};
// Arrays:
list = [1, 2, 3, 4, 5];
// Objects:
math = {
root: Math.sqrt,
square: square,
cube: function(x) {
return x * square(x);
}
};
// Splats:
race = function(winner, ...runners) {
return print(winner, runners);
};
if (typeof elvis !== "undefined" && elvis !== null) {
// Existence:
alert("I knew it!");
}
// Array comprehensions:
cubes = (function() {
var i, len, results;
results = [];
for (i = 0, len = list.length; i < len; i++) {
num = list[i];
results.push(math.cube(num));
}
return results;
})();
cubes
COFFEESCRIPT 2
WHAT’S NEW IN COFFEESCRIPT 2?
The biggest change in CoffeeScript 2 is that now the CoffeeScript compiler
produces modern JavaScript syntax (ES6, or ES2015 and later). A CoffeeScript =>
becomes a JS =>, a CoffeeScript class becomes a JS class and so on. Major new
features in CoffeeScript 2 include async functions and JSX. You can read more in
the announcement.
There are very few breaking changes from CoffeeScript 1.x to 2; we hope the
upgrade process is smooth for most projects.
COMPATIBILITY
Most modern JavaScript features that CoffeeScript supports can run natively in
Node 7.6+, meaning that Node can run CoffeeScript’s output without any further
processing required. Here are some notable exceptions:
* JSX always requires transpilation.
* Splats, a.k.a. object rest/spread syntax, for objects are supported by Node
8.6+.
* The regular expression s (dotall) flag is supported by Node 9+.
* Async generator functions are supported by Node 10+.
* Modules are supported by Node 12+ with "type": "module" in your project’s
package.json.
This list may be incomplete, and excludes versions of Node that support newer
features behind flags; please refer to node.green for full details. You can run
the tests in your browser to see what your browser supports. It is your
responsibility to ensure that your runtime supports the modern features you use;
or that you transpile your code. When in doubt, transpile.
For compatibility with other JavaScript frameworks and tools, see Integrations.
INSTALLATION
The command-line version of coffee is available as a Node.js utility, requiring
Node 6 or later. The core compiler however, does not depend on Node, and can be
run in any JavaScript environment, or in the browser (see Try CoffeeScript).
To install, first make sure you have a working copy of the latest stable version
of Node.js. You can then install CoffeeScript globally with npm:
> npm install --global coffeescript
This will make the coffee and cake commands available globally.
If you are using CoffeeScript in a project, you should install it locally for
that project so that the version of CoffeeScript is tracked as one of your
project’s dependencies. Within that project’s folder:
> npm install --save-dev coffeescript
The coffee and cake commands will first look in the current folder to see if
CoffeeScript is installed locally, and use that version if so. This allows
different versions of CoffeeScript to be installed globally and locally.
If you plan to use the --transpile option (see Transpilation) you will need to
also install @babel/core either globally or locally, depending on whether you
are running a globally or locally installed version of CoffeeScript.
USAGE
COMMAND LINE
Once installed, you should have access to the coffee command, which can execute
scripts, compile .coffee files into .js, and provide an interactive REPL. The
coffee command takes the following options:
Option Description -c, --compile Compile a .coffee script into a .js JavaScript
file of the same name. -t, --transpile Pipe the CoffeeScript compiler’s output
through Babel before saving or running the generated JavaScript. Requires
@babel/core to be installed, and options to pass to Babel in a .babelrc file or
a package.json with a babel key in the path of the file or folder to be
compiled. See Transpilation. -m, --map Generate source maps alongside the
compiled JavaScript files. Adds sourceMappingURL directives to the JavaScript as
well. -M, --inline-map Just like --map, but include the source map directly in
the compiled JavaScript files, rather than in a separate file. -i, --interactive
Launch an interactive CoffeeScript session to try short snippets. Identical to
calling coffee with no arguments. -o, --output [DIR] Write out all compiled
JavaScript files into the specified directory. Use in conjunction with --compile
or --watch. -w, --watch Watch files for changes, rerunning the specified command
when any file is updated. -p, --print Instead of writing out the JavaScript as a
file, print it directly to stdout. -s, --stdio Pipe in CoffeeScript to STDIN and
get back JavaScript over STDOUT. Good for use with processes written in other
languages. An example:
cat src/cake.coffee | coffee -sc -l, --literate Parses the code as Literate
CoffeeScript. You only need to specify this when passing in code directly over
stdio, or using some sort of extension-less file name. -e, --eval Compile and
print a little snippet of CoffeeScript directly from the command line. For
example:
coffee -e "console.log num for num in [10..1]" -r, --require [MODULE] require()
the given module before starting the REPL or evaluating the code given with the
--eval flag. -b, --bare Compile the JavaScript without the top-level function
safety wrapper. --no-header Suppress the “Generated by CoffeeScript” header.
--nodejs The node executable has some useful options you can set, such as
--debug, --debug-brk, --max-stack-size, and --expose-gc. Use this flag to
forward options directly to Node.js. To pass multiple flags, use --nodejs
multiple times. --ast Generate an abstract syntax tree of nodes of the
CoffeeScript. Used for integrating with JavaScript build tools. --tokens Instead
of parsing the CoffeeScript, just lex it, and print out the token stream. Used
for debugging the compiler. -n, --nodes Instead of compiling the CoffeeScript,
just lex and parse it, and print out the parse tree. Used for debugging the
compiler.
EXAMPLES:
* Compile a directory tree of .coffee files in src into a parallel tree of .js
files in lib:
coffee --compile --output lib/ src/
* Watch a file for changes, and recompile it every time the file is saved:
coffee --watch --compile experimental.coffee
* Concatenate a list of files into a single script:
coffee --join project.js --compile src/*.coffee
* Print out the compiled JS from a one-liner:
coffee -bpe "alert i for i in [0..10]"
* All together now, watch and recompile an entire project as you work on it:
coffee -o lib/ -cw src/
* Start the CoffeeScript REPL (Ctrl-D to exit, Ctrl-Vfor multi-line):
coffee
To use --transpile, see Transpilation.
NODE.JS
If you’d like to use Node.js’ CommonJS to require CoffeeScript files, e.g.
require './app.coffee', you must first “register” CoffeeScript as an extension:
> require 'coffeescript/register'
>
> App = require './app' # The .coffee extension is optional
If you want to use the compiler’s API, for example to make an app that compiles
strings of CoffeeScript on the fly, you can require the full module:
> CoffeeScript = require 'coffeescript'
>
> eval CoffeeScript.compile 'console.log "Mmmmm, I could really go for some #{Math.pi}"'
The compile method has the signature compile(code, options) where code is a
string of CoffeeScript code, and the optional options is an object with some or
all of the following properties:
* options.sourceMap, boolean: if true, a source map will be generated; and
instead of returning a string, compile will return an object of the form {js,
v3SourceMap, sourceMap}.
* options.inlineMap, boolean: if true, output the source map as a
base64-encoded string in a comment at the bottom.
* options.filename, string: the filename to use for the source map. It can
include a path (relative or absolute).
* options.bare, boolean: if true, output without the top-level function safety
wrapper.
* options.header, boolean: if true, output the Generated by CoffeeScript
header.
* options.transpile, object: if set, this must be an object with the options to
pass to Babel. See Transpilation.
* options.ast, boolean: if true, return an abstract syntax tree of the input
CoffeeScript source code.
TRANSPILATION
CoffeeScript 2 generates JavaScript that uses the latest, modern syntax. The
runtime or browsers where you want your code to run might not support all of
that syntax. In that case, we want to convert modern JavaScript into older
JavaScript that will run in older versions of Node or older browsers; for
example, { a } = obj into a = obj.a. This is done via transpilers like Babel,
Bublé or Traceur Compiler. See Build Tools.
QUICKSTART
From the root of your project:
> npm install --save-dev @babel/core @babel/preset-env
> echo '{ "presets": ["@babel/env"] }' > .babelrc
> coffee --compile --transpile --inline-map some-file.coffee
TRANSPILING WITH THE COFFEESCRIPT COMPILER
To make things easy, CoffeeScript has built-in support for the popular Babel
transpiler. You can use it via the --transpile command-line option or the
transpile Node API option. To use either, @babel/core must be installed in your
project:
> npm install --save-dev @babel/core
Or if you’re running the coffee command outside of a project folder, using a
globally-installed coffeescript module, @babel/core needs to be installed
globally:
> npm install --global @babel/core
By default, Babel doesn’t do anything—it doesn’t make assumptions about what you
want to transpile to. You need to provide it with a configuration so that it
knows what to do. One way to do this is by creating a .babelrc file in the
folder containing the files you’re compiling, or in any parent folder up the
path above those files. (Babel supports other ways, too.) A minimal .babelrc
file would be just { "presets": ["@babel/env"] }. This implies that you have
installed @babel/preset-env:
> npm install --save-dev @babel/preset-env # Or --global for non-project-based usage
See Babel’s website to learn about presets and plugins and the multitude of
options you have. Another preset you might need is
@babel/plugin-transform-react-jsx if you’re using JSX with React (JSX can also
be used with other frameworks).
Once you have @babel/core and @babel/preset-env (or other presets or plugins)
installed, and a .babelrc file (or other equivalent) in place, you can use
coffee --transpile to pipe CoffeeScript’s output through Babel using the options
you’ve saved.
If you’re using CoffeeScript via the Node API, where you call
CoffeeScript.compile with a string to be compiled and an options object, the
transpile key of the options object should be the Babel options:
> CoffeeScript.compile(code, {transpile: {presets: ['@babel/env']}})
You can also transpile CoffeeScript’s output without using the transpile option,
for example as part of a build chain. This lets you use transpilers other than
Babel, and it gives you greater control over the process. There are many great
task runners for setting up JavaScript build chains, such as Gulp, Webpack,
Grunt and Broccoli.
POLYFILLS
Note that transpiling doesn’t automatically supply polyfills for your code.
CoffeeScript itself will output Array.indexOf if you use the in operator, or
destructuring or spread/rest syntax; and Function.bind if you use a bound (=>)
method in a class. Both are supported in Internet Explorer 9+ and all more
recent browsers, but you will need to supply polyfills if you need to support
Internet Explorer 8 or below and are using features that would cause these
methods to be output. You’ll also need to supply polyfills if your own code uses
these methods or another method added in recent versions of JavaScript. One
polyfill option is @babel/polyfill, though there are many other strategies.
LANGUAGE REFERENCE
This reference is structured so that it can be read from top to bottom, if you
like. Later sections use ideas and syntax previously introduced. Familiarity
with JavaScript is assumed. In all of the following examples, the source
CoffeeScript is provided on the left, and the direct compilation into JavaScript
is on the right.
Many of the examples can be run (where it makes sense) by pressing the ▶ button
on the right. The CoffeeScript on the left is editable, and the JavaScript will
update as you edit.
First, the basics: CoffeeScript uses significant whitespace to delimit blocks of
code. You don’t need to use semicolons ; to terminate expressions, ending the
line will do just as well (although semicolons can still be used to fit multiple
expressions onto a single line). Instead of using curly braces { } to surround
blocks of code in functions, if-statements, switch, and try/catch, use
indentation.
You don’t need to use parentheses to invoke a function if you’re passing
arguments. The implicit call wraps forward to the end of the line or block
expression.
console.log sys.inspect object → console.log(sys.inspect(object));
FUNCTIONS
Functions are defined by an optional list of parameters in parentheses, an
arrow, and the function body. The empty function looks like this: ->
square = (x) -> x * x cube = (x) -> square(x) * x
square = (x) -> x * x
cube = (x) -> square(x) * x
var cube, square; square = function(x) { return x * x; }; cube = function(x) {
return square(x) * x; };
var cube, square;
square = function(x) {
return x * x;
};
cube = function(x) {
return square(x) * x;
};
cube(5)
Functions may also have default values for arguments, which will be used if the
incoming argument is missing (undefined).
fill = (container, liquid = "coffee") -> "Filling the #{container} with
#{liquid}..."
fill = (container, liquid = "coffee") ->
"Filling the #{container} with #{liquid}..."
var fill; fill = function(container, liquid = "coffee") { return `Filling the
${container} with ${liquid}...`; };
var fill;
fill = function(container, liquid = "coffee") {
return `Filling the ${container} with ${liquid}...`;
};
fill("cup")
STRINGS
Like JavaScript and many other languages, CoffeeScript supports strings as
delimited by the " or ' characters. CoffeeScript also supports string
interpolation within "-quoted strings, using #{ … }. Single-quoted strings are
literal. You may even use interpolation in object keys.
author = "Wittgenstein" quote = "A picture is a fact. -- #{ author }" sentence =
"#{ 22 / 7 } is a decent approximation of π"
author = "Wittgenstein"
quote = "A picture is a fact. -- #{ author }"
sentence = "#{ 22 / 7 } is a decent approximation of π"
var author, quote, sentence; author = "Wittgenstein"; quote = `A picture is a
fact. -- ${author}`; sentence = `${22 / 7} is a decent approximation of π`;
var author, quote, sentence;
author = "Wittgenstein";
quote = `A picture is a fact. -- ${author}`;
sentence = `${22 / 7} is a decent approximation of π`;
sentence
Multiline strings are allowed in CoffeeScript. Lines are joined by a single
space unless they end with a backslash. Indentation is ignored.
mobyDick = "Call me Ishmael. Some years ago -- never mind how long precisely --
having little or no money in my purse, and nothing particular to interest me on
shore, I thought I would sail about a little and see the watery part of the
world..."
mobyDick = "Call me Ishmael. Some years ago --
never mind how long precisely -- having little
or no money in my purse, and nothing particular
to interest me on shore, I thought I would sail
about a little and see the watery part of the
world..."
var mobyDick; mobyDick = "Call me Ishmael. Some years ago -- never mind how long
precisely -- having little or no money in my purse, and nothing particular to
interest me on shore, I thought I would sail about a little and see the watery
part of the world...";
var mobyDick;
mobyDick = "Call me Ishmael. Some years ago -- never mind how long precisely -- having little or no money in my purse, and nothing particular to interest me on shore, I thought I would sail about a little and see the watery part of the world...";
mobyDick
Block strings, delimited by """ or ''', can be used to hold formatted or
indentation-sensitive text (or, if you just don’t feel like escaping quotes and
apostrophes). The indentation level that begins the block is maintained
throughout, so you can keep it all aligned with the body of your code.
html = """ <strong> cup of coffeescript </strong> """
html = """
<strong>
cup of coffeescript
</strong>
"""
var html; html = `<strong> cup of coffeescript </strong>`;
var html;
html = `<strong>
cup of coffeescript
</strong>`;
html
Double-quoted block strings, like other double-quoted strings, allow
interpolation.
OBJECTS AND ARRAYS
The CoffeeScript literals for objects and arrays look very similar to their
JavaScript cousins. When each property is listed on its own line, the commas are
optional. Objects may be created using indentation instead of explicit braces,
similar to YAML.
song = ["do", "re", "mi", "fa", "so"] singers = {Jagger: "Rock", Elvis: "Roll"}
bitlist = [ 1, 0, 1 0, 0, 1 1, 1, 0 ] kids = brother: name: "Max" age: 11
sister: name: "Ida" age: 9
song = ["do", "re", "mi", "fa", "so"]
singers = {Jagger: "Rock", Elvis: "Roll"}
bitlist = [
1, 0, 1
0, 0, 1
1, 1, 0
]
kids =
brother:
name: "Max"
age: 11
sister:
name: "Ida"
age: 9
var bitlist, kids, singers, song; song = ["do", "re", "mi", "fa", "so"]; singers
= { Jagger: "Rock", Elvis: "Roll" }; bitlist = [1, 0, 1, 0, 0, 1, 1, 1, 0]; kids
= { brother: { name: "Max", age: 11 }, sister: { name: "Ida", age: 9 } };
var bitlist, kids, singers, song;
song = ["do", "re", "mi", "fa", "so"];
singers = {
Jagger: "Rock",
Elvis: "Roll"
};
bitlist = [1, 0, 1, 0, 0, 1, 1, 1, 0];
kids = {
brother: {
name: "Max",
age: 11
},
sister: {
name: "Ida",
age: 9
}
};
song.join(" … ")
CoffeeScript has a shortcut for creating objects when you want the key to be set
with a variable of the same name. Note that the { and } are required for this
shorthand.
name = "Michelangelo" mask = "orange" weapon = "nunchuks" turtle = {name, mask,
weapon} output = "#{turtle.name} wears an #{turtle.mask} mask. Watch out for his
#{turtle.weapon}!"
name = "Michelangelo"
mask = "orange"
weapon = "nunchuks"
turtle = {name, mask, weapon}
output = "#{turtle.name} wears an #{turtle.mask} mask. Watch out for his #{turtle.weapon}!"
var mask, name, output, turtle, weapon; name = "Michelangelo"; mask = "orange";
weapon = "nunchuks"; turtle = {name, mask, weapon}; output = `${turtle.name}
wears an ${turtle.mask} mask. Watch out for his ${turtle.weapon}!`;
var mask, name, output, turtle, weapon;
name = "Michelangelo";
mask = "orange";
weapon = "nunchuks";
turtle = {name, mask, weapon};
output = `${turtle.name} wears an ${turtle.mask} mask. Watch out for his ${turtle.weapon}!`;
COMMENTS
In CoffeeScript, comments are denoted by the # character to the end of a line,
or from ### to the next appearance of ###. Comments are ignored by the compiler,
though the compiler makes its best effort at reinserting your comments into the
output JavaScript after compilation.
### Fortune Cookie Reader v1.0 Released under the MIT License ### sayFortune =
(fortune) -> console.log fortune # in bed!
###
Fortune Cookie Reader v1.0
Released under the MIT License
###
sayFortune = (fortune) ->
console.log fortune # in bed!
/* Fortune Cookie Reader v1.0 Released under the MIT License */ var sayFortune;
sayFortune = function(fortune) { return console.log(fortune); // in bed! };
/*
Fortune Cookie Reader v1.0
Released under the MIT License
*/
var sayFortune;
sayFortune = function(fortune) {
return console.log(fortune); // in bed!
};
Inline ### comments make type annotations possible.
LEXICAL SCOPING AND VARIABLE SAFETY
The CoffeeScript compiler takes care to make sure that all of your variables are
properly declared within lexical scope — you never need to write var yourself.
outer = 1 changeNumbers = -> inner = -1 outer = 10 inner = changeNumbers()
outer = 1
changeNumbers = ->
inner = -1
outer = 10
inner = changeNumbers()
var changeNumbers, inner, outer; outer = 1; changeNumbers = function() { var
inner; inner = -1; return outer = 10; }; inner = changeNumbers();
var changeNumbers, inner, outer;
outer = 1;
changeNumbers = function() {
var inner;
inner = -1;
return outer = 10;
};
inner = changeNumbers();
inner
Notice how all of the variable declarations have been pushed up to the top of
the closest scope, the first time they appear. outer is not redeclared within
the inner function, because it’s already in scope; inner within the function, on
the other hand, should not be able to change the value of the external variable
of the same name, and therefore has a declaration of its own.
Because you don’t have direct access to the var keyword, it’s impossible to
shadow an outer variable on purpose, you may only refer to it. So be careful
that you’re not reusing the name of an external variable accidentally, if you’re
writing a deeply nested function.
Although suppressed within this documentation for clarity, all CoffeeScript
output (except in files with import or export statements) is wrapped in an
anonymous function: (function(){ … })();. This safety wrapper, combined with the
automatic generation of the var keyword, make it exceedingly difficult to
pollute the global namespace by accident. (The safety wrapper can be disabled
with the bare option, and is unnecessary and automatically disabled when using
modules.)
If you’d like to create top-level variables for other scripts to use, attach
them as properties on window; attach them as properties on the exports object in
CommonJS; or use an export statement. If you’re targeting both CommonJS and the
browser, the existential operator (covered below), gives you a reliable way to
figure out where to add them: exports ? this.
Since CoffeeScript takes care of all variable declaration, it is not possible to
declare variables with ES2015’s let or const. This is intentional; we feel that
the simplicity gained by not having to think about variable declaration
outweighs the benefit of having three separate ways to declare variables.
IF, ELSE, UNLESS, AND CONDITIONAL ASSIGNMENT
if/else statements can be written without the use of parentheses and curly
brackets. As with functions and other block expressions, multi-line conditionals
are delimited by indentation. There’s also a handy postfix form, with the if or
unless at the end.
CoffeeScript can compile if statements into JavaScript expressions, using the
ternary operator when possible, and closure wrapping otherwise. There is no
explicit ternary statement in CoffeeScript — you simply use a regular if
statement on a single line.
mood = greatlyImproved if singing if happy and knowsIt clapsHands() chaChaCha()
else showIt() date = if friday then sue else jill
mood = greatlyImproved if singing
if happy and knowsIt
clapsHands()
chaChaCha()
else
showIt()
date = if friday then sue else jill
var date, mood; if (singing) { mood = greatlyImproved; } if (happy && knowsIt) {
clapsHands(); chaChaCha(); } else { showIt(); } date = friday ? sue : jill;
var date, mood;
if (singing) {
mood = greatlyImproved;
}
if (happy && knowsIt) {
clapsHands();
chaChaCha();
} else {
showIt();
}
date = friday ? sue : jill;
SPLATS, OR REST PARAMETERS/SPREAD SYNTAX
The JavaScript arguments object is a useful way to work with functions that
accept variable numbers of arguments. CoffeeScript provides splats ..., both for
function definition as well as invocation, making variable numbers of arguments
a little bit more palatable. ES2015 adopted this feature as their rest
parameters.
gold = silver = rest = "unknown" awardMedals = (first, second, others...) ->
gold = first silver = second rest = others contenders = [ "Michael Phelps" "Liu
Xiang" "Yao Ming" "Allyson Felix" "Shawn Johnson" "Roman Sebrle" "Guo Jingjing"
"Tyson Gay" "Asafa Powell" "Usain Bolt" ] awardMedals contenders... alert """
Gold: #{gold} Silver: #{silver} The Field: #{rest.join ', '} """
gold = silver = rest = "unknown"
awardMedals = (first, second, others...) ->
gold = first
silver = second
rest = others
contenders = [
"Michael Phelps"
"Liu Xiang"
"Yao Ming"
"Allyson Felix"
"Shawn Johnson"
"Roman Sebrle"
"Guo Jingjing"
"Tyson Gay"
"Asafa Powell"
"Usain Bolt"
]
awardMedals contenders...
alert """
Gold: #{gold}
Silver: #{silver}
The Field: #{rest.join ', '}
"""
var awardMedals, contenders, gold, rest, silver; gold = silver = rest =
"unknown"; awardMedals = function(first, second, ...others) { gold = first;
silver = second; return rest = others; }; contenders = ["Michael Phelps", "Liu
Xiang", "Yao Ming", "Allyson Felix", "Shawn Johnson", "Roman Sebrle", "Guo
Jingjing", "Tyson Gay", "Asafa Powell", "Usain Bolt"];
awardMedals(...contenders); alert(`Gold: ${gold} Silver: ${silver} The Field:
${rest.join(', ')}`);
var awardMedals, contenders, gold, rest, silver;
gold = silver = rest = "unknown";
awardMedals = function(first, second, ...others) {
gold = first;
silver = second;
return rest = others;
};
contenders = ["Michael Phelps", "Liu Xiang", "Yao Ming", "Allyson Felix", "Shawn Johnson", "Roman Sebrle", "Guo Jingjing", "Tyson Gay", "Asafa Powell", "Usain Bolt"];
awardMedals(...contenders);
alert(`Gold: ${gold}
Silver: ${silver}
The Field: ${rest.join(', ')}`);
Splats also let us elide array elements…
popular = ['pepperoni', 'sausage', 'cheese'] unwanted = ['anchovies', 'olives']
all = [popular..., unwanted..., 'mushrooms']
popular = ['pepperoni', 'sausage', 'cheese']
unwanted = ['anchovies', 'olives']
all = [popular..., unwanted..., 'mushrooms']
var all, popular, unwanted; popular = ['pepperoni', 'sausage', 'cheese'];
unwanted = ['anchovies', 'olives']; all = [...popular, ...unwanted,
'mushrooms'];
var all, popular, unwanted;
popular = ['pepperoni', 'sausage', 'cheese'];
unwanted = ['anchovies', 'olives'];
all = [...popular, ...unwanted, 'mushrooms'];
all
…and object properties.
user = name: 'Werner Heisenberg' occupation: 'theoretical physicist' currentUser
= { user..., status: 'Uncertain' }
user =
name: 'Werner Heisenberg'
occupation: 'theoretical physicist'
currentUser = { user..., status: 'Uncertain' }
var currentUser, user; user = { name: 'Werner Heisenberg', occupation:
'theoretical physicist' }; currentUser = { ...user, status: 'Uncertain' };
var currentUser, user;
user = {
name: 'Werner Heisenberg',
occupation: 'theoretical physicist'
};
currentUser = {
...user,
status: 'Uncertain'
};
JSON.stringify(currentUser)
In ECMAScript this is called spread syntax, and has been supported for arrays
since ES2015 and objects since ES2018.
LOOPS AND COMPREHENSIONS
Most of the loops you’ll write in CoffeeScript will be comprehensions over
arrays, objects, and ranges. Comprehensions replace (and compile into) for
loops, with optional guard clauses and the value of the current array index.
Unlike for loops, array comprehensions are expressions, and can be returned and
assigned.
# Eat lunch. eat = (food) -> "#{food} eaten." eat food for food in ['toast',
'cheese', 'wine'] # Fine five course dining. courses = ['greens', 'caviar',
'truffles', 'roast', 'cake'] menu = (i, dish) -> "Menu Item #{i}: #{dish}" menu
i + 1, dish for dish, i in courses # Health conscious meal. foods = ['broccoli',
'spinach', 'chocolate'] eat food for food in foods when food isnt 'chocolate'
# Eat lunch.
eat = (food) -> "#{food} eaten."
eat food for food in ['toast', 'cheese', 'wine']
# Fine five course dining.
courses = ['greens', 'caviar', 'truffles', 'roast', 'cake']
menu = (i, dish) -> "Menu Item #{i}: #{dish}"
menu i + 1, dish for dish, i in courses
# Health conscious meal.
foods = ['broccoli', 'spinach', 'chocolate']
eat food for food in foods when food isnt 'chocolate'
// Eat lunch. var courses, dish, eat, food, foods, i, j, k, l, len, len1, len2,
menu, ref; eat = function(food) { return `${food} eaten.`; }; ref = ['toast',
'cheese', 'wine']; for (j = 0, len = ref.length; j < len; j++) { food = ref[j];
eat(food); } // Fine five course dining. courses = ['greens', 'caviar',
'truffles', 'roast', 'cake']; menu = function(i, dish) { return `Menu Item ${i}:
${dish}`; }; for (i = k = 0, len1 = courses.length; k < len1; i = ++k) { dish =
courses[i]; menu(i + 1, dish); } // Health conscious meal. foods = ['broccoli',
'spinach', 'chocolate']; for (l = 0, len2 = foods.length; l < len2; l++) { food
= foods[l]; if (food !== 'chocolate') { eat(food); } }
// Eat lunch.
var courses, dish, eat, food, foods, i, j, k, l, len, len1, len2, menu, ref;
eat = function(food) {
return `${food} eaten.`;
};
ref = ['toast', 'cheese', 'wine'];
for (j = 0, len = ref.length; j < len; j++) {
food = ref[j];
eat(food);
}
// Fine five course dining.
courses = ['greens', 'caviar', 'truffles', 'roast', 'cake'];
menu = function(i, dish) {
return `Menu Item ${i}: ${dish}`;
};
for (i = k = 0, len1 = courses.length; k < len1; i = ++k) {
dish = courses[i];
menu(i + 1, dish);
}
// Health conscious meal.
foods = ['broccoli', 'spinach', 'chocolate'];
for (l = 0, len2 = foods.length; l < len2; l++) {
food = foods[l];
if (food !== 'chocolate') {
eat(food);
}
}
Comprehensions should be able to handle most places where you otherwise would
use a loop, each/forEach, map, or select/filter, for example:
shortNames = (name for name in list when name.length < 5)
If you know the start and end of your loop, or would like to step through in
fixed-size increments, you can use a range to specify the start and end of your
comprehension.
countdown = (num for num in [10..1])
countdown = (num for num in [10..1])
var countdown, num; countdown = (function() { var i, results; results = []; for
(num = i = 10; i >= 1; num = --i) { results.push(num); } return results; })();
var countdown, num;
countdown = (function() {
var i, results;
results = [];
for (num = i = 10; i >= 1; num = --i) {
results.push(num);
}
return results;
})();
countdown
Note how because we are assigning the value of the comprehensions to a variable
in the example above, CoffeeScript is collecting the result of each iteration
into an array. Sometimes functions end with loops that are intended to run only
for their side-effects. Be careful that you’re not accidentally returning the
results of the comprehension in these cases, by adding a meaningful return value
— like true — or null, to the bottom of your function.
To step through a range comprehension in fixed-size chunks, use by, for example:
evens = (x for x in [0..10] by 2)
If you don’t need the current iteration value you may omit it:
browser.closeCurrentTab() for [0...count]
Comprehensions can also be used to iterate over the keys and values in an
object. Use of to signal comprehension over the properties of an object instead
of the values in an array.
yearsOld = max: 10, ida: 9, tim: 11 ages = for child, age of yearsOld "#{child}
is #{age}"
yearsOld = max: 10, ida: 9, tim: 11
ages = for child, age of yearsOld
"#{child} is #{age}"
var age, ages, child, yearsOld; yearsOld = { max: 10, ida: 9, tim: 11 }; ages =
(function() { var results; results = []; for (child in yearsOld) { age =
yearsOld[child]; results.push(`${child} is ${age}`); } return results; })();
var age, ages, child, yearsOld;
yearsOld = {
max: 10,
ida: 9,
tim: 11
};
ages = (function() {
var results;
results = [];
for (child in yearsOld) {
age = yearsOld[child];
results.push(`${child} is ${age}`);
}
return results;
})();
ages.join(", ")
If you would like to iterate over just the keys that are defined on the object
itself, by adding a hasOwnProperty check to avoid properties that may be
inherited from the prototype, use for own key, value of object.
To iterate a generator function, use from. See Generator Functions.
The only low-level loop that CoffeeScript provides is the while loop. The main
difference from JavaScript is that the while loop can be used as an expression,
returning an array containing the result of each iteration through the loop.
# Econ 101 if this.studyingEconomics buy() while supply > demand sell() until
supply > demand # Nursery Rhyme num = 6 lyrics = while num -= 1 "#{num} little
monkeys, jumping on the bed. One fell out and bumped his head."
# Econ 101
if this.studyingEconomics
buy() while supply > demand
sell() until supply > demand
# Nursery Rhyme
num = 6
lyrics = while num -= 1
"#{num} little monkeys, jumping on the bed.
One fell out and bumped his head."
// Econ 101 var lyrics, num; if (this.studyingEconomics) { while (supply >
demand) { buy(); } while (!(supply > demand)) { sell(); } } // Nursery Rhyme num
= 6; lyrics = (function() { var results; results = []; while (num -= 1) {
results.push(`${num} little monkeys, jumping on the bed. One fell out and bumped
his head.`); } return results; })();
// Econ 101
var lyrics, num;
if (this.studyingEconomics) {
while (supply > demand) {
buy();
}
while (!(supply > demand)) {
sell();
}
}
// Nursery Rhyme
num = 6;
lyrics = (function() {
var results;
results = [];
while (num -= 1) {
results.push(`${num} little monkeys, jumping on the bed. One fell out and bumped his head.`);
}
return results;
})();
lyrics.join("\n")
For readability, the until keyword is equivalent to while not, and the loop
keyword is equivalent to while true.
When using a JavaScript loop to generate functions, it’s common to insert a
closure wrapper in order to ensure that loop variables are closed over, and all
the generated functions don’t just share the final values. CoffeeScript provides
the do keyword, which immediately invokes a passed function, forwarding any
arguments.
for filename in list do (filename) -> if filename not in ['.DS_Store',
'Thumbs.db', 'ehthumbs.db'] fs.readFile filename, (err, contents) -> compile
filename, contents.toString()
for filename in list
do (filename) ->
if filename not in ['.DS_Store', 'Thumbs.db', 'ehthumbs.db']
fs.readFile filename, (err, contents) ->
compile filename, contents.toString()
var filename, i, len; for (i = 0, len = list.length; i < len; i++) { filename =
list[i]; (function(filename) { if (filename !== '.DS_Store' && filename !==
'Thumbs.db' && filename !== 'ehthumbs.db') { return fs.readFile(filename,
function(err, contents) { return compile(filename, contents.toString()); }); }
})(filename); }
var filename, i, len;
for (i = 0, len = list.length; i < len; i++) {
filename = list[i];
(function(filename) {
if (filename !== '.DS_Store' && filename !== 'Thumbs.db' && filename !== 'ehthumbs.db') {
return fs.readFile(filename, function(err, contents) {
return compile(filename, contents.toString());
});
}
})(filename);
}
ARRAY SLICING AND SPLICING WITH RANGES
Ranges can also be used to extract slices of arrays. With two dots (3..6), the
range is inclusive (3, 4, 5, 6); with three dots (3...6), the range excludes the
end (3, 4, 5). Slices indices have useful defaults. An omitted first index
defaults to zero and an omitted second index defaults to the size of the array.
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9] start = numbers[0..2] middle =
numbers[3...-2] end = numbers[-2..] copy = numbers[..]
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]
start = numbers[0..2]
middle = numbers[3...-2]
end = numbers[-2..]
copy = numbers[..]
var copy, end, middle, numbers, start; numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];
start = numbers.slice(0, 3); middle = numbers.slice(3, -2); end =
numbers.slice(-2); copy = numbers.slice(0);
var copy, end, middle, numbers, start;
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];
start = numbers.slice(0, 3);
middle = numbers.slice(3, -2);
end = numbers.slice(-2);
copy = numbers.slice(0);
middle
The same syntax can be used with assignment to replace a segment of an array
with new values, splicing it.
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] numbers[3..6] = [-3, -4, -5, -6]
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
numbers[3..6] = [-3, -4, -5, -6]
var numbers, ref, splice = [].splice; numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
splice.apply(numbers, [3, 4].concat(ref = [-3, -4, -5, -6])), ref;
var numbers, ref,
splice = [].splice;
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
splice.apply(numbers, [3, 4].concat(ref = [-3, -4, -5, -6])), ref;
numbers
Note that JavaScript strings are immutable, and can’t be spliced.
EVERYTHING IS AN EXPRESSION (AT LEAST, AS MUCH AS POSSIBLE)
You might have noticed how even though we don’t add return statements to
CoffeeScript functions, they nonetheless return their final value. The
CoffeeScript compiler tries to make sure that all statements in the language can
be used as expressions. Watch how the return gets pushed down into each possible
branch of execution in the function below.
grade = (student) -> if student.excellentWork "A+" else if student.okayStuff if
student.triedHard then "B" else "B-" else "C" eldest = if 24 > 21 then "Liz"
else "Ike"
grade = (student) ->
if student.excellentWork
"A+"
else if student.okayStuff
if student.triedHard then "B" else "B-"
else
"C"
eldest = if 24 > 21 then "Liz" else "Ike"
var eldest, grade; grade = function(student) { if (student.excellentWork) {
return "A+"; } else if (student.okayStuff) { if (student.triedHard) { return
"B"; } else { return "B-"; } } else { return "C"; } }; eldest = 24 > 21 ? "Liz"
: "Ike";
var eldest, grade;
grade = function(student) {
if (student.excellentWork) {
return "A+";
} else if (student.okayStuff) {
if (student.triedHard) {
return "B";
} else {
return "B-";
}
} else {
return "C";
}
};
eldest = 24 > 21 ? "Liz" : "Ike";
eldest
Even though functions will always return their final value, it’s both possible
and encouraged to return early from a function body writing out the explicit
return (return value), when you know that you’re done.
Because variable declarations occur at the top of scope, assignment can be used
within expressions, even for variables that haven’t been seen before:
six = (one = 1) + (two = 2) + (three = 3)
six = (one = 1) + (two = 2) + (three = 3)
var one, six, three, two; six = (one = 1) + (two = 2) + (three = 3);
var one, six, three, two;
six = (one = 1) + (two = 2) + (three = 3);
six
Things that would otherwise be statements in JavaScript, when used as part of an
expression in CoffeeScript, are converted into expressions by wrapping them in a
closure. This lets you do useful things, like assign the result of a
comprehension to a variable:
# The first ten global properties. globals = (name for name of window)[0...10]
# The first ten global properties.
globals = (name for name of window)[0...10]
// The first ten global properties. var globals, name; globals = ((function() {
var results; results = []; for (name in window) { results.push(name); } return
results; })()).slice(0, 10);
// The first ten global properties.
var globals, name;
globals = ((function() {
var results;
results = [];
for (name in window) {
results.push(name);
}
return results;
})()).slice(0, 10);
globals
As well as silly things, like passing a try/catch statement directly into a
function call:
alert( try nonexistent / undefined catch error "And the error is ... #{error}" )
alert(
try
nonexistent / undefined
catch error
"And the error is ... #{error}"
)
var error; alert((function() { try { return nonexistent / void 0; } catch
(error1) { error = error1; return `And the error is ... ${error}`; } })());
var error;
alert((function() {
try {
return nonexistent / void 0;
} catch (error1) {
error = error1;
return `And the error is ... ${error}`;
}
})());
There are a handful of statements in JavaScript that can’t be meaningfully
converted into expressions, namely break, continue, and return. If you make use
of them within a block of code, CoffeeScript won’t try to perform the
conversion.
OPERATORS AND ALIASES
Because the == operator frequently causes undesirable coercion, is intransitive,
and has a different meaning than in other languages, CoffeeScript compiles ==
into ===, and != into !==. In addition, is compiles into ===, and isnt into !==.
You can use not as an alias for !.
For logic, and compiles to &&, and or into ||.
Instead of a newline or semicolon, then can be used to separate conditions from
expressions, in while, if/else, and switch/when statements.
As in YAML, on and yes are the same as boolean true, while off and no are
boolean false.
unless can be used as the inverse of if.
As a shortcut for this.property, you can use @property.
You can use in to test for array presence, and of to test for JavaScript
object-key presence.
In a for loop, from compiles to the ES2015 of. (Yes, it’s unfortunate; the
CoffeeScript of predates the ES2015 of.)
To simplify math expressions, ** can be used for exponentiation and // performs
floor division. % works just like in JavaScript, while %% provides “dividend
dependent modulo”:
-7 % 5 == -2 # The remainder of 7 / 5 -7 %% 5 == 3 # n %% 5 is always between 0
and 4 tabs.selectTabAtIndex((tabs.currentIndex - count) %% tabs.length)
-7 % 5 == -2 # The remainder of 7 / 5
-7 %% 5 == 3 # n %% 5 is always between 0 and 4
tabs.selectTabAtIndex((tabs.currentIndex - count) %% tabs.length)
var modulo = function(a, b) { return (+a % (b = +b) + b) % b; }; -7 % 5 === -2;
// The remainder of 7 / 5 modulo(-7, 5) === 3; // n %% 5 is always between 0 and
4 tabs.selectTabAtIndex(modulo(tabs.currentIndex - count, tabs.length));
var modulo = function(a, b) { return (+a % (b = +b) + b) % b; };
-7 % 5 === -2; // The remainder of 7 / 5
modulo(-7, 5) === 3; // n %% 5 is always between 0 and 4
tabs.selectTabAtIndex(modulo(tabs.currentIndex - count, tabs.length));
All together now:
CoffeeScript JavaScript is === isnt !== not ! and && or || true, yes, on true
false, no, off false @, this this a in b [].indexOf.call(b, a) >= 0 a of b a in
b for a from b for (a of b) a ** b a ** b a // b Math.floor(a / b) a %% b (a % b
+ b) % b
launch() if ignition is on volume = 10 if band isnt SpinalTap
letTheWildRumpusBegin() unless answer is no if car.speed < limit then
accelerate() winner = yes if pick in [47, 92, 13] print inspect "My name is
#{@name}"
launch() if ignition is on
volume = 10 if band isnt SpinalTap
letTheWildRumpusBegin() unless answer is no
if car.speed < limit then accelerate()
winner = yes if pick in [47, 92, 13]
print inspect "My name is #{@name}"
var volume, winner; if (ignition === true) { launch(); } if (band !== SpinalTap)
{ volume = 10; } if (answer !== false) { letTheWildRumpusBegin(); } if
(car.speed < limit) { accelerate(); } if (pick === 47 || pick === 92 || pick ===
13) { winner = true; } print(inspect(`My name is ${this.name}`));
var volume, winner;
if (ignition === true) {
launch();
}
if (band !== SpinalTap) {
volume = 10;
}
if (answer !== false) {
letTheWildRumpusBegin();
}
if (car.speed < limit) {
accelerate();
}
if (pick === 47 || pick === 92 || pick === 13) {
winner = true;
}
print(inspect(`My name is ${this.name}`));
THE EXISTENTIAL OPERATOR
It’s a little difficult to check for the existence of a variable in JavaScript.
if (variable) … comes close, but fails for zero, the empty string, and false (to
name just the most common cases). CoffeeScript’s existential operator ? returns
true unless a variable is null or undefined or undeclared, which makes it
analogous to Ruby’s nil?.
It can also be used for safer conditional assignment than the JavaScript pattern
a = a || value provides, for cases where you may be handling numbers or strings.
solipsism = true if mind? and not world? speed = 0 speed ?= 15 footprints = yeti
? "bear"
solipsism = true if mind? and not world?
speed = 0
speed ?= 15
footprints = yeti ? "bear"
var footprints, solipsism, speed; if ((typeof mind !== "undefined" && mind !==
null) && (typeof world === "undefined" || world === null)) { solipsism = true; }
speed = 0; if (speed == null) { speed = 15; } footprints = typeof yeti !==
"undefined" && yeti !== null ? yeti : "bear";
var footprints, solipsism, speed;
if ((typeof mind !== "undefined" && mind !== null) && (typeof world === "undefined" || world === null)) {
solipsism = true;
}
speed = 0;
if (speed == null) {
speed = 15;
}
footprints = typeof yeti !== "undefined" && yeti !== null ? yeti : "bear";
footprints
Note that if the compiler knows that a is in scope and therefore declared, a?
compiles to a != null, not a !== null. The != makes a loose comparison to null,
which does double duty also comparing against undefined. The reverse also holds
for not a? or unless a?.
major = 'Computer Science' unless major? signUpForClass 'Introduction to Wines'
major = 'Computer Science'
unless major?
signUpForClass 'Introduction to Wines'
var major; major = 'Computer Science'; if (major == null) {
signUpForClass('Introduction to Wines'); }
var major;
major = 'Computer Science';
if (major == null) {
signUpForClass('Introduction to Wines');
}
If a variable might be undeclared, the compiler does a thorough check. This is
what JavaScript coders should be typing when they want to check if a mystery
variable exists.
if window? environment = 'browser (probably)'
if window?
environment = 'browser (probably)'
var environment; if (typeof window !== "undefined" && window !== null) {
environment = 'browser (probably)'; }
var environment;
if (typeof window !== "undefined" && window !== null) {
environment = 'browser (probably)';
}
The accessor variant of the existential operator ?. can be used to soak up null
references in a chain of properties. Use it instead of the dot accessor . in
cases where the base value may be null or undefined. If all of the properties
exist then you’ll get the expected result, if the chain is broken, undefined is
returned instead of the TypeError that would be raised otherwise.
zip = lottery.drawWinner?().address?.zipcode
zip = lottery.drawWinner?().address?.zipcode
var ref, zip; zip = typeof lottery.drawWinner === "function" ? (ref =
lottery.drawWinner().address) != null ? ref.zipcode : void 0 : void 0;
var ref, zip;
zip = typeof lottery.drawWinner === "function" ? (ref = lottery.drawWinner().address) != null ? ref.zipcode : void 0 : void 0;
For completeness:
Example Definition a? tests that a is in scope and a != null a ? b returns a if
a is in scope and a != null; otherwise, b a?.b or a?['b'] returns a.b if a is in
scope and a != null; otherwise, undefined a?(b, c) or a? b, c returns the
result of calling a (with arguments b and c) if a is in scope and callable;
otherwise, undefined a ?= b assigns the value of b to a if a is not in scope or
if a == null; produces the new value of a
CHAINING FUNCTION CALLS
Leading . closes all open calls, allowing for simpler chaining syntax.
$ 'body' .click (e) -> $ '.box' .fadeIn 'fast' .addClass 'show' .css
'background', 'white'
$ 'body'
.click (e) ->
$ '.box'
.fadeIn 'fast'
.addClass 'show'
.css 'background', 'white'
$('body').click(function(e) { return $('.box').fadeIn('fast').addClass('show');
}).css('background', 'white');
$('body').click(function(e) {
return $('.box').fadeIn('fast').addClass('show');
}).css('background', 'white');
DESTRUCTURING ASSIGNMENT
Just like JavaScript (since ES2015), CoffeeScript has destructuring assignment
syntax. When you assign an array or object literal to a value, CoffeeScript
breaks up and matches both sides against each other, assigning the values on the
right to the variables on the left. In the simplest case, it can be used for
parallel assignment:
theBait = 1000 theSwitch = 0 [theBait, theSwitch] = [theSwitch, theBait]
theBait = 1000
theSwitch = 0
[theBait, theSwitch] = [theSwitch, theBait]
var theBait, theSwitch; theBait = 1000; theSwitch = 0; [theBait, theSwitch] =
[theSwitch, theBait];
var theBait, theSwitch;
theBait = 1000;
theSwitch = 0;
[theBait, theSwitch] = [theSwitch, theBait];
theBait
But it’s also helpful for dealing with functions that return multiple values.
weatherReport = (location) -> # Make an Ajax request to fetch the weather...
[location, 72, "Mostly Sunny"] [city, temp, forecast] = weatherReport "Berkeley,
CA"
weatherReport = (location) ->
# Make an Ajax request to fetch the weather...
[location, 72, "Mostly Sunny"]
[city, temp, forecast] = weatherReport "Berkeley, CA"
var city, forecast, temp, weatherReport; weatherReport = function(location) { //
Make an Ajax request to fetch the weather... return [location, 72, "Mostly
Sunny"]; }; [city, temp, forecast] = weatherReport("Berkeley, CA");
var city, forecast, temp, weatherReport;
weatherReport = function(location) {
// Make an Ajax request to fetch the weather...
return [location, 72, "Mostly Sunny"];
};
[city, temp, forecast] = weatherReport("Berkeley, CA");
forecast
Destructuring assignment can be used with any depth of array and object nesting,
to help pull out deeply nested properties.
futurists = sculptor: "Umberto Boccioni" painter: "Vladimir Burliuk" poet: name:
"F.T. Marinetti" address: [ "Via Roma 42R" "Bellagio, Italy 22021" ] {sculptor}
= futurists {poet: {name, address: [street, city]}} = futurists
futurists =
sculptor: "Umberto Boccioni"
painter: "Vladimir Burliuk"
poet:
name: "F.T. Marinetti"
address: [
"Via Roma 42R"
"Bellagio, Italy 22021"
]
{sculptor} = futurists
{poet: {name, address: [street, city]}} = futurists
var city, futurists, name, sculptor, street; futurists = { sculptor: "Umberto
Boccioni", painter: "Vladimir Burliuk", poet: { name: "F.T. Marinetti", address:
["Via Roma 42R", "Bellagio, Italy 22021"] } }; ({sculptor} = futurists); ({
poet: { name, address: [street, city] } } = futurists);
var city, futurists, name, sculptor, street;
futurists = {
sculptor: "Umberto Boccioni",
painter: "Vladimir Burliuk",
poet: {
name: "F.T. Marinetti",
address: ["Via Roma 42R", "Bellagio, Italy 22021"]
}
};
({sculptor} = futurists);
({
poet: {
name,
address: [street, city]
}
} = futurists);
name + "-" + street
Destructuring assignment can even be combined with splats.
tag = "<impossible>" [open, contents..., close] = tag.split("")
tag = "<impossible>"
[open, contents..., close] = tag.split("")
var close, contents, open, ref, tag, splice = [].splice; tag = "<impossible>";
ref = tag.split(""), [open, ...contents] = ref, [close] = splice.call(contents,
-1);
var close, contents, open, ref, tag,
splice = [].splice;
tag = "<impossible>";
ref = tag.split(""), [open, ...contents] = ref, [close] = splice.call(contents, -1);
contents.join("")
Expansion can be used to retrieve elements from the end of an array without
having to assign the rest of its values. It works in function parameter lists as
well.
text = "Every literary critic believes he will outwit history and have the last
word" [first, ..., last] = text.split " "
text = "Every literary critic believes he will
outwit history and have the last word"
[first, ..., last] = text.split " "
var first, last, ref, text, slice = [].slice; text = "Every literary critic
believes he will outwit history and have the last word"; ref = text.split(" "),
[first] = ref, [last] = slice.call(ref, -1);
var first, last, ref, text,
slice = [].slice;
text = "Every literary critic believes he will outwit history and have the last word";
ref = text.split(" "), [first] = ref, [last] = slice.call(ref, -1);
first + " " + last
Destructuring assignment is also useful when combined with class constructors to
assign properties to your instance from an options object passed to the
constructor.
class Person constructor: (options) -> {@name, @age, @height = 'average'} =
options tim = new Person name: 'Tim', age: 4
class Person
constructor: (options) ->
{@name, @age, @height = 'average'} = options
tim = new Person name: 'Tim', age: 4
var Person, tim; Person = class Person { constructor(options) { ({name:
this.name, age: this.age, height: this.height = 'average'} = options); } }; tim
= new Person({ name: 'Tim', age: 4 });
var Person, tim;
Person = class Person {
constructor(options) {
({name: this.name, age: this.age, height: this.height = 'average'} = options);
}
};
tim = new Person({
name: 'Tim',
age: 4
});
tim.age + " " + tim.height
The above example also demonstrates that if properties are missing in the
destructured object or array, you can, just like in JavaScript, provide
defaults. Note though that unlike with the existential operator, the default is
only applied with the value is missing or undefined—passing null will set a
value of null, not the default.
BOUND (FAT ARROW) FUNCTIONS
In JavaScript, the this keyword is dynamically scoped to mean the object that
the current function is attached to. If you pass a function as a callback or
attach it to a different object, the original value of this will be lost. If
you’re not familiar with this behavior, this Digital Web article gives a good
overview of the quirks.
The fat arrow => can be used to both define a function, and to bind it to the
current value of this, right on the spot. This is helpful when using
callback-based libraries like Prototype or jQuery, for creating iterator
functions to pass to each, or event-handler functions to use with on. Functions
created with the fat arrow are able to access properties of the this where
they’re defined.
Account = (customer, cart) -> @customer = customer @cart = cart
$('.shopping_cart').on 'click', (event) => @customer.purchase @cart
Account = (customer, cart) ->
@customer = customer
@cart = cart
$('.shopping_cart').on 'click', (event) =>
@customer.purchase @cart
var Account; Account = function(customer, cart) { this.customer = customer;
this.cart = cart; return $('.shopping_cart').on('click', (event) => { return
this.customer.purchase(this.cart); }); };
var Account;
Account = function(customer, cart) {
this.customer = customer;
this.cart = cart;
return $('.shopping_cart').on('click', (event) => {
return this.customer.purchase(this.cart);
});
};
If we had used -> in the callback above, @customer would have referred to the
undefined “customer” property of the DOM element, and trying to call purchase()
on it would have raised an exception.
The fat arrow was one of the most popular features of CoffeeScript, and ES2015
adopted it; so CoffeeScript 2 compiles => to ES =>.
GENERATOR FUNCTIONS
CoffeeScript supports ES2015 generator functions through the yield keyword.
There’s no function*(){} nonsense — a generator in CoffeeScript is simply a
function that yields.
perfectSquares = -> num = 0 loop num += 1 yield num * num return window.ps or=
perfectSquares()
perfectSquares = ->
num = 0
loop
num += 1
yield num * num
return
window.ps or= perfectSquares()
var perfectSquares; perfectSquares = function*() { var num; num = 0; while
(true) { num += 1; yield num * num; } }; window.ps || (window.ps =
perfectSquares());
var perfectSquares;
perfectSquares = function*() {
var num;
num = 0;
while (true) {
num += 1;
yield num * num;
}
};
window.ps || (window.ps = perfectSquares());
ps.next().value
yield* is called yield from, and yield return may be used if you need to force a
generator that doesn’t yield.
You can iterate over a generator function using for…from.
fibonacci = -> [previous, current] = [1, 1] loop [previous, current] = [current,
previous + current] yield current return getFibonacciNumbers = (length) ->
results = [1] for n from fibonacci() results.push n break if results.length is
length results
fibonacci = ->
[previous, current] = [1, 1]
loop
[previous, current] = [current, previous + current]
yield current
return
getFibonacciNumbers = (length) ->
results = [1]
for n from fibonacci()
results.push n
break if results.length is length
results
var fibonacci, getFibonacciNumbers; fibonacci = function*() { var current,
previous; [previous, current] = [1, 1]; while (true) { [previous, current] =
[current, previous + current]; yield current; } }; getFibonacciNumbers =
function(length) { var n, results; results = [1]; for (n of fibonacci()) {
results.push(n); if (results.length === length) { break; } } return results; };
var fibonacci, getFibonacciNumbers;
fibonacci = function*() {
var current, previous;
[previous, current] = [1, 1];
while (true) {
[previous, current] = [current, previous + current];
yield current;
}
};
getFibonacciNumbers = function(length) {
var n, results;
results = [1];
for (n of fibonacci()) {
results.push(n);
if (results.length === length) {
break;
}
}
return results;
};
getFibonacciNumbers(10)
ASYNC FUNCTIONS
ES2017’s async functions are supported through the await keyword. Like with
generators, there’s no need for an async keyword; an async function in
CoffeeScript is simply a function that awaits.
Similar to how yield return forces a generator, await return may be used to
force a function to be async.
# Your browser must support async/await and speech synthesis # to run this
example. sleep = (ms) -> new Promise (resolve) -> window.setTimeout resolve, ms
say = (text) -> window.speechSynthesis.cancel() window.speechSynthesis.speak new
SpeechSynthesisUtterance text countdown = (seconds) -> for i in [seconds..1] say
i await sleep 1000 # wait one second say "Blastoff!" countdown 3
# Your browser must support async/await and speech synthesis
# to run this example.
sleep = (ms) ->
new Promise (resolve) ->
window.setTimeout resolve, ms
say = (text) ->
window.speechSynthesis.cancel()
window.speechSynthesis.speak new SpeechSynthesisUtterance text
countdown = (seconds) ->
for i in [seconds..1]
say i
await sleep 1000 # wait one second
say "Blastoff!"
countdown 3
// Your browser must support async/await and speech synthesis // to run this
example. var countdown, say, sleep; sleep = function(ms) { return new
Promise(function(resolve) { return window.setTimeout(resolve, ms); }); }; say =
function(text) { window.speechSynthesis.cancel(); return
window.speechSynthesis.speak(new SpeechSynthesisUtterance(text)); }; countdown =
async function(seconds) { var i, j, ref; for (i = j = ref = seconds; (ref <= 1 ?
j <= 1 : j >= 1); i = ref <= 1 ? ++j : --j) { say(i); await sleep(1000); // wait
one second } return say("Blastoff!"); }; countdown(3);
// Your browser must support async/await and speech synthesis
// to run this example.
var countdown, say, sleep;
sleep = function(ms) {
return new Promise(function(resolve) {
return window.setTimeout(resolve, ms);
});
};
say = function(text) {
window.speechSynthesis.cancel();
return window.speechSynthesis.speak(new SpeechSynthesisUtterance(text));
};
countdown = async function(seconds) {
var i, j, ref;
for (i = j = ref = seconds; (ref <= 1 ? j <= 1 : j >= 1); i = ref <= 1 ? ++j : --j) {
say(i);
await sleep(1000); // wait one second
}
return say("Blastoff!");
};
countdown(3);
CLASSES
CoffeeScript 1 provided the class and extends keywords as syntactic sugar for
working with prototypal functions. With ES2015, JavaScript has adopted those
keywords; so CoffeeScript 2 compiles its class and extends keywords to ES2015
classes.
class Animal constructor: (@name) -> move: (meters) -> alert @name + " moved
#{meters}m." class Snake extends Animal move: -> alert "Slithering..." super 5
class Horse extends Animal move: -> alert "Galloping..." super 45 sam = new
Snake "Sammy the Python" tom = new Horse "Tommy the Palomino" sam.move()
tom.move()
class Animal
constructor: (@name) ->
move: (meters) ->
alert @name + " moved #{meters}m."
class Snake extends Animal
move: ->
alert "Slithering..."
super 5
class Horse extends Animal
move: ->
alert "Galloping..."
super 45
sam = new Snake "Sammy the Python"
tom = new Horse "Tommy the Palomino"
sam.move()
tom.move()
var Animal, Horse, Snake, sam, tom; Animal = class Animal { constructor(name) {
this.name = name; } move(meters) { return alert(this.name + ` moved
${meters}m.`); } }; Snake = class Snake extends Animal { move() {
alert("Slithering..."); return super.move(5); } }; Horse = class Horse extends
Animal { move() { alert("Galloping..."); return super.move(45); } }; sam = new
Snake("Sammy the Python"); tom = new Horse("Tommy the Palomino"); sam.move();
tom.move();
var Animal, Horse, Snake, sam, tom;
Animal = class Animal {
constructor(name) {
this.name = name;
}
move(meters) {
return alert(this.name + ` moved ${meters}m.`);
}
};
Snake = class Snake extends Animal {
move() {
alert("Slithering...");
return super.move(5);
}
};
Horse = class Horse extends Animal {
move() {
alert("Galloping...");
return super.move(45);
}
};
sam = new Snake("Sammy the Python");
tom = new Horse("Tommy the Palomino");
sam.move();
tom.move();
Static methods can be defined using @ before the method name:
class Teenager @say: (speech) -> words = speech.split ' ' fillers = ['uh', 'um',
'like', 'actually', 'so', 'maybe'] output = [] for word, index in words
output.push word output.push fillers[Math.floor(Math.random() * fillers.length)]
unless index is words.length - 1 output.join ', '
class Teenager
@say: (speech) ->
words = speech.split ' '
fillers = ['uh', 'um', 'like', 'actually', 'so', 'maybe']
output = []
for word, index in words
output.push word
output.push fillers[Math.floor(Math.random() * fillers.length)] unless index is words.length - 1
output.join ', '
var Teenager; Teenager = class Teenager { static say(speech) { var fillers, i,
index, len, output, word, words; words = speech.split(' '); fillers = ['uh',
'um', 'like', 'actually', 'so', 'maybe']; output = []; for (index = i = 0, len =
words.length; i < len; index = ++i) { word = words[index]; output.push(word); if
(index !== words.length - 1) { output.push(fillers[Math.floor(Math.random() *
fillers.length)]); } } return output.join(', '); } };
var Teenager;
Teenager = class Teenager {
static say(speech) {
var fillers, i, index, len, output, word, words;
words = speech.split(' ');
fillers = ['uh', 'um', 'like', 'actually', 'so', 'maybe'];
output = [];
for (index = i = 0, len = words.length; i < len; index = ++i) {
word = words[index];
output.push(word);
if (index !== words.length - 1) {
output.push(fillers[Math.floor(Math.random() * fillers.length)]);
}
}
return output.join(', ');
}
};
Teenager.say("Are we there yet?")
Finally, class definitions are blocks of executable code, which make for
interesting metaprogramming possibilities. In the context of a class definition,
this is the class object itself; therefore, you can assign static properties by
using @property: value.
PROTOTYPAL INHERITANCE
In addition to supporting ES2015 classes, CoffeeScript provides a shortcut for
working with prototypes. The :: operator gives you quick access to an object’s
prototype:
String::dasherize = -> this.replace /_/g, "-"
String::dasherize = ->
this.replace /_/g, "-"
String.prototype.dasherize = function() { return this.replace(/_/g, "-"); };
String.prototype.dasherize = function() {
return this.replace(/_/g, "-");
};
"one_two".dasherize()
SWITCH/WHEN/ELSE
switch statements in JavaScript are a bit awkward. You need to remember to break
at the end of every case statement to avoid accidentally falling through to the
default case. CoffeeScript prevents accidental fall-through, and can convert the
switch into a returnable, assignable expression. The format is: switch
condition, when clauses, else the default case.
As in Ruby, switch statements in CoffeeScript can take multiple values for each
when clause. If any of the values match, the clause runs.
switch day when "Mon" then go work when "Tue" then go relax when "Thu" then go
iceFishing when "Fri", "Sat" if day is bingoDay go bingo go dancing when "Sun"
then go church else go work
switch day
when "Mon" then go work
when "Tue" then go relax
when "Thu" then go iceFishing
when "Fri", "Sat"
if day is bingoDay
go bingo
go dancing
when "Sun" then go church
else go work
switch (day) { case "Mon": go(work); break; case "Tue": go(relax); break; case
"Thu": go(iceFishing); break; case "Fri": case "Sat": if (day === bingoDay) {
go(bingo); go(dancing); } break; case "Sun": go(church); break; default:
go(work); }
switch (day) {
case "Mon":
go(work);
break;
case "Tue":
go(relax);
break;
case "Thu":
go(iceFishing);
break;
case "Fri":
case "Sat":
if (day === bingoDay) {
go(bingo);
go(dancing);
}
break;
case "Sun":
go(church);
break;
default:
go(work);
}
switch statements can also be used without a control expression, turning them in
to a cleaner alternative to if/else chains.
score = 76 grade = switch when score < 60 then 'F' when score < 70 then 'D' when
score < 80 then 'C' when score < 90 then 'B' else 'A' # grade == 'C'
score = 76
grade = switch
when score < 60 then 'F'
when score < 70 then 'D'
when score < 80 then 'C'
when score < 90 then 'B'
else 'A'
# grade == 'C'
var grade, score; score = 76; grade = (function() { switch (false) { case
!(score < 60): return 'F'; case !(score < 70): return 'D'; case !(score < 80):
return 'C'; case !(score < 90): return 'B'; default: return 'A'; } })(); //
grade == 'C'
var grade, score;
score = 76;
grade = (function() {
switch (false) {
case !(score < 60):
return 'F';
case !(score < 70):
return 'D';
case !(score < 80):
return 'C';
case !(score < 90):
return 'B';
default:
return 'A';
}
})();
// grade == 'C'
TRY/CATCH/FINALLY
try expressions have the same semantics as try statements in JavaScript, though
in CoffeeScript, you may omit both the catch and finally parts. The catch part
may also omit the error parameter if it is not needed.
try allHellBreaksLoose() catsAndDogsLivingTogether() catch error print error
finally cleanUp()
try
allHellBreaksLoose()
catsAndDogsLivingTogether()
catch error
print error
finally
cleanUp()
var error; try { allHellBreaksLoose(); catsAndDogsLivingTogether(); } catch
(error1) { error = error1; print(error); } finally { cleanUp(); }
var error;
try {
allHellBreaksLoose();
catsAndDogsLivingTogether();
} catch (error1) {
error = error1;
print(error);
} finally {
cleanUp();
}
CHAINED COMPARISONS
CoffeeScript borrows chained comparisons from Python — making it easy to test if
a value falls within a certain range.
cholesterol = 127 healthy = 200 > cholesterol > 60
cholesterol = 127
healthy = 200 > cholesterol > 60
var cholesterol, healthy; cholesterol = 127; healthy = (200 > cholesterol &&
cholesterol > 60);
var cholesterol, healthy;
cholesterol = 127;
healthy = (200 > cholesterol && cholesterol > 60);
healthy
BLOCK REGULAR EXPRESSIONS
Similar to block strings and comments, CoffeeScript supports block regexes —
extended regular expressions that ignore internal whitespace and can contain
comments and interpolation. Modeled after Perl’s /x modifier, CoffeeScript’s
block regexes are delimited by /// and go a long way towards making complex
regular expressions readable. To quote from the CoffeeScript source:
NUMBER = /// ^ 0b[01]+ | # binary ^ 0o[0-7]+ | # octal ^ 0x[\da-f]+ | # hex ^
\d*\.?\d+ (?:e[+-]?\d+)? # decimal ///i
NUMBER = ///
^ 0b[01]+ | # binary
^ 0o[0-7]+ | # octal
^ 0x[\da-f]+ | # hex
^ \d*\.?\d+ (?:e[+-]?\d+)? # decimal
///i
var NUMBER; NUMBER = /^0b[01]+|^0o[0-7]+|^0x[\da-f]+|^\d*\.?\d+(?:e[+-]?\d+)?/i;
// binary // octal // hex // decimal
var NUMBER;
NUMBER = /^0b[01]+|^0o[0-7]+|^0x[\da-f]+|^\d*\.?\d+(?:e[+-]?\d+)?/i; // binary
// octal
// hex
// decimal
TAGGED TEMPLATE LITERALS
CoffeeScript supports ES2015 tagged template literals, which enable customized
string interpolation. If you immediately prefix a string with a function name
(no space between the two), CoffeeScript will output this “function plus string”
combination as an ES2015 tagged template literal, which will behave accordingly:
the function is called, with the parameters being the input text and expression
parts that make up the interpolated string. The function can then assemble these
parts into an output string, providing custom string interpolation.
upperCaseExpr = (textParts, expressions...) -> textParts.reduce (text, textPart,
i) -> text + expressions[i - 1].toUpperCase() + textPart greet = (name,
adjective) -> upperCaseExpr""" Hi #{name}. You look #{adjective}! """
upperCaseExpr = (textParts, expressions...) ->
textParts.reduce (text, textPart, i) ->
text + expressions[i - 1].toUpperCase() + textPart
greet = (name, adjective) ->
upperCaseExpr"""
Hi #{name}. You look #{adjective}!
"""
var greet, upperCaseExpr; upperCaseExpr = function(textParts, ...expressions) {
return textParts.reduce(function(text, textPart, i) { return text +
expressions[i - 1].toUpperCase() + textPart; }); }; greet = function(name,
adjective) { return upperCaseExpr`Hi ${name}. You look ${adjective}!`; };
var greet, upperCaseExpr;
upperCaseExpr = function(textParts, ...expressions) {
return textParts.reduce(function(text, textPart, i) {
return text + expressions[i - 1].toUpperCase() + textPart;
});
};
greet = function(name, adjective) {
return upperCaseExpr`Hi ${name}. You look ${adjective}!`;
};
greet("greg", "awesome")
MODULES
ES2015 modules are supported in CoffeeScript, with very similar import and
export syntax:
import './local-file.js' # Must be the filename of the generated file import
'package' import _ from 'underscore' import * as underscore from 'underscore'
import { now } from 'underscore' import { now as currentTimestamp } from
'underscore' import { first, last } from 'underscore' import utilityBelt, { each
} from 'underscore' import dates from './calendar.json' assert { type: 'json' }
export default Math export square = (x) -> x * x export class Mathematics least:
(x, y) -> if x < y then x else y export { sqrt } export { sqrt as squareRoot }
export { Mathematics as default, sqrt as squareRoot } export * from 'underscore'
export { max, min } from 'underscore' export { version } from './package.json'
assert { type: 'json' }
import './local-file.js' # Must be the filename of the generated file
import 'package'
import _ from 'underscore'
import * as underscore from 'underscore'
import { now } from 'underscore'
import { now as currentTimestamp } from 'underscore'
import { first, last } from 'underscore'
import utilityBelt, { each } from 'underscore'
import dates from './calendar.json' assert { type: 'json' }
export default Math
export square = (x) -> x * x
export class Mathematics
least: (x, y) -> if x < y then x else y
export { sqrt }
export { sqrt as squareRoot }
export { Mathematics as default, sqrt as squareRoot }
export * from 'underscore'
export { max, min } from 'underscore'
export { version } from './package.json' assert { type: 'json' }
import './local-file.js'; import 'package'; import _ from 'underscore'; import *
as underscore from 'underscore'; import { now } from 'underscore'; import { now
as currentTimestamp } from 'underscore'; import { first, last } from
'underscore'; import utilityBelt, { each } from 'underscore'; import dates from
'./calendar.json' assert { type: 'json' }; export default Math; export var
square = function(x) { return x * x; }; export var Mathematics = class
Mathematics { least(x, y) { if (x < y) { return x; } else { return y; } } };
export { sqrt }; export { sqrt as squareRoot }; export { Mathematics as default,
sqrt as squareRoot }; export * from 'underscore'; export { max, min } from
'underscore'; export { version } from './package.json' assert { type: 'json' };
import './local-file.js';
import 'package';
import _ from 'underscore';
import * as underscore from 'underscore';
import {
now
} from 'underscore';
import {
now as currentTimestamp
} from 'underscore';
import {
first,
last
} from 'underscore';
import utilityBelt, {
each
} from 'underscore';
import dates from './calendar.json' assert {
type: 'json'
};
export default Math;
export var square = function(x) {
return x * x;
};
export var Mathematics = class Mathematics {
least(x, y) {
if (x < y) {
return x;
} else {
return y;
}
}
};
export {
sqrt
};
export {
sqrt as squareRoot
};
export {
Mathematics as default,
sqrt as squareRoot
};
export * from 'underscore';
export {
max,
min
} from 'underscore';
export {
version
} from './package.json' assert {
type: 'json'
};
Dynamic import is also supported, with mandatory parentheses:
# Your browser must support dynamic import to run this example. do -> { run } =
await import('./browser-compiler-modern/coffeescript.js') run ''' if 5 < new
Date().getHours() < 9 alert 'Time to make the coffee!' else alert 'Time to get
some work done.' '''
# Your browser must support dynamic import to run this example.
do ->
{ run } = await import('./browser-compiler-modern/coffeescript.js')
run '''
if 5 < new Date().getHours() < 9
alert 'Time to make the coffee!'
else
alert 'Time to get some work done.'
'''
// Your browser must support dynamic import to run this example. (async
function() { var run; ({run} = (await
import('./browser-compiler-modern/coffeescript.js'))); return run(`if 5 < new
Date().getHours() < 9 alert 'Time to make the coffee!' else alert 'Time to get
some work done.'`); })();
// Your browser must support dynamic import to run this example.
(async function() {
var run;
({run} = (await import('./browser-compiler-modern/coffeescript.js')));
return run(`if 5 < new Date().getHours() < 9
alert 'Time to make the coffee!'
else
alert 'Time to get some work done.'`);
})();
Note that the CoffeeScript compiler does not resolve modules; writing an import
or export statement in CoffeeScript will produce an import or export statement
in the resulting output. Such statements can be run by all modern browsers (when
the script is referenced via <script type="module">) and by Node.js when the
output .js files are in a folder where the nearest parent package.json file
contains "type": "module". Because the runtime is evaluating the generated
output, the import statements must reference the output files; so if file.coffee
is output as file.js, it needs to be referenced as file.js in the import
statement, with the .js extension included.
Also, any file with an import or export statement will be output without a
top-level function safety wrapper; in other words, importing or exporting
modules will automatically trigger bare mode for that file. This is because per
the ES2015 spec, import or export statements must occur at the topmost scope.
EMBEDDED JAVASCRIPT
Hopefully, you’ll never need to use it, but if you ever need to intersperse
snippets of JavaScript within your CoffeeScript, you can use backticks to pass
it straight through.
hi = `function() { return [document.title, "Hello JavaScript"].join(": "); }`
hi = `function() {
return [document.title, "Hello JavaScript"].join(": ");
}`
var hi; hi = function() { return [document.title, "Hello JavaScript"].join(":
"); };
var hi;
hi = function() {
return [document.title, "Hello JavaScript"].join(": ");
};
hi()
Escape backticks with backslashes: \` becomes ` .
Escape backslashes before backticks with more backslashes: \\\` becomes \` .
markdown = `function () { return \`In Markdown, write code like \\\`this\\\`\`;
}`
markdown = `function () {
return \`In Markdown, write code like \\\`this\\\`\`;
}`
var markdown; markdown = function () { return `In Markdown, write code like
\`this\``; };
var markdown;
markdown = function () {
return `In Markdown, write code like \`this\``;
};
markdown()
You can also embed blocks of JavaScript using triple backticks. That’s easier
than escaping backticks, if you need them inside your JavaScript block.
``` function time() { return `The time is ${new Date().toLocaleTimeString()}`; }
```
```
function time() {
return `The time is ${new Date().toLocaleTimeString()}`;
}
```
function time() { return `The time is ${new Date().toLocaleTimeString()}`; } ;
function time() {
return `The time is ${new Date().toLocaleTimeString()}`;
}
;
time()
JSX
JSX is JavaScript containing interspersed XML elements. While conceived for
React, it is not specific to any particular library or framework.
CoffeeScript supports interspersed XML elements, without the need for separate
plugins or special settings. The XML elements will be compiled as such,
outputting JSX that could be parsed like any normal JSX file, for example by
Babel with the React JSX transform. CoffeeScript does not output
React.createElement calls or any code specific to React or any other framework.
It is up to you to attach another step in your build chain to convert this JSX
to whatever function calls you wish the XML elements to compile to.
Just like in JSX and HTML, denote XML tags using < and >. You can interpolate
CoffeeScript code inside a tag using { and }. To avoid compiler errors, when
using < and > to mean “less than” or “greater than,” you should wrap the
operators in spaces to distinguish them from XML tags. So i < len, not i<len.
The compiler tries to be forgiving when it can be sure what you intend, but
always putting spaces around the “less than” and “greater than” operators will
remove ambiguity.
renderStarRating = ({ rating, maxStars }) -> <aside title={"Rating: #{rating} of
#{maxStars} stars"}> {for wholeStar in [0...Math.floor(rating)] <Star
className="wholeStar" key={wholeStar} />} {if rating % 1 isnt 0 <Star
className="halfStar" />} {for emptyStar in [Math.ceil(rating)...maxStars] <Star
className="emptyStar" key={emptyStar} />} </aside>
renderStarRating = ({ rating, maxStars }) ->
<aside title={"Rating: #{rating} of #{maxStars} stars"}>
{for wholeStar in [0...Math.floor(rating)]
<Star className="wholeStar" key={wholeStar} />}
{if rating % 1 isnt 0
<Star className="halfStar" />}
{for emptyStar in [Math.ceil(rating)...maxStars]
<Star className="emptyStar" key={emptyStar} />}
</aside>
var renderStarRating; renderStarRating = function({rating, maxStars}) { var
emptyStar, wholeStar; return <aside title={`Rating: ${rating} of ${maxStars}
stars`}> {(function() { var i, ref, results; results = []; for (wholeStar = i =
0, ref = Math.floor(rating); (0 <= ref ? i < ref : i > ref); wholeStar = 0 <=
ref ? ++i : --i) { results.push(<Star className="wholeStar" key={wholeStar} />);
} return results; })()} {rating % 1 !== 0 ? <Star className="halfStar" /> : void
0} {(function() { var i, ref, ref1, results; results = []; for (emptyStar = i =
ref = Math.ceil(rating), ref1 = maxStars; (ref <= ref1 ? i < ref1 : i > ref1);
emptyStar = ref <= ref1 ? ++i : --i) { results.push(<Star className="emptyStar"
key={emptyStar} />); } return results; })()} </aside>; };
var renderStarRating;
renderStarRating = function({rating, maxStars}) {
var emptyStar, wholeStar;
return <aside title={`Rating: ${rating} of ${maxStars} stars`}>
{(function() {
var i, ref, results;
results = [];
for (wholeStar = i = 0, ref = Math.floor(rating); (0 <= ref ? i < ref : i > ref); wholeStar = 0 <= ref ? ++i : --i) {
results.push(<Star className="wholeStar" key={wholeStar} />);
}
return results;
})()}
{rating % 1 !== 0 ? <Star className="halfStar" /> : void 0}
{(function() {
var i, ref, ref1, results;
results = [];
for (emptyStar = i = ref = Math.ceil(rating), ref1 = maxStars; (ref <= ref1 ? i < ref1 : i > ref1); emptyStar = ref <= ref1 ? ++i : --i) {
results.push(<Star className="emptyStar" key={emptyStar} />);
}
return results;
})()}
</aside>;
};
Older plugins or forks of CoffeeScript supported JSX syntax and referred to it
as CSX or CJSX. They also often used a .cjsx file extension, but this is no
longer necessary; regular .coffee will do.
TYPE ANNOTATIONS
Static type checking can be achieved in CoffeeScript by using Flow’s Comment
Types syntax:
# @flow ###:: type Obj = { num: number, }; ### fn = (str ###: string ###, obj
###: Obj ###) ###: string ### -> str + obj.num
# @flow
###::
type Obj = {
num: number,
};
###
fn = (str ###: string ###, obj ###: Obj ###) ###: string ### ->
str + obj.num
// @flow /*:: type Obj = { num: number, }; */ var fn; fn = function(str/*:
string */, obj/*: Obj */)/*: string */ { return str + obj.num; };
// @flow
/*::
type Obj = {
num: number,
};
*/
var fn;
fn = function(str/*: string */, obj/*: Obj */)/*: string */ {
return str + obj.num;
};
CoffeeScript does not do any type checking itself; the JavaScript output you see
above needs to get passed to Flow for it to validate your code. We expect most
people will use a build tool for this, but here’s how to do it the simplest way
possible using the CoffeeScript and Flow command-line tools, assuming you’ve
already installed Flow and the latest CoffeeScript in your project folder:
> coffee --bare --no-header --compile app.coffee && npm run flow
--bare and --no-header are important because Flow requires the first line of the
file to be the comment // @flow. If you configure your build chain to compile
CoffeeScript and pass the result to Flow in-memory, you can get better
performance than this example; and a proper build tool should be able to watch
your CoffeeScript files and recompile and type-check them for you on save.
If you know of another way to achieve static type checking with CoffeeScript,
please create an issue and let us know.
LITERATE COFFEESCRIPT
Besides being used as an ordinary programming language, CoffeeScript may also be
written in “literate” mode. If you name your file with a .litcoffee extension,
you can write it as a Markdown document — a document that also happens to be
executable CoffeeScript code. The compiler will treat any indented blocks
(Markdown’s way of indicating source code) as executable code, and ignore the
rest as comments. Code blocks must also be separated from comments by at least
one blank line.
Just for kicks, a little bit of the compiler is currently implemented in this
fashion: See it as a document, raw, and properly highlighted in a text editor.
A few caveats:
* Code blocks need to maintain consistent indentation relative to each other.
When the compiler parses your Literate CoffeeScript file, it first discards
all the non-code block lines and then parses the remainder as a regular
CoffeeScript file. Therefore the code blocks need to be written as if the
comment lines don’t exist, with consistent indentation (including whether
they are indented with tabs or spaces).
* Along those lines, code blocks within list items or blockquotes are not
treated as executable code. Since list items and blockquotes imply their own
indentation, it would be ambiguous how to treat indentation between
successive code blocks when some are within these other blocks and some are
not.
* List items can be at most only one paragraph long. The second paragraph of a
list item would be indented after a blank line, and therefore
indistinguishable from a code block.
SOURCE MAPS
CoffeeScript includes support for generating source maps, a way to tell your
JavaScript engine what part of your CoffeeScript program matches up with the
code being evaluated. Browsers that support it can automatically use source maps
to show your original source code in the debugger. To generate source maps
alongside your JavaScript files, pass the --map or -m flag to the compiler.
For a full introduction to source maps, how they work, and how to hook them up
in your browser, read the HTML5 Tutorial.
CAKE, AND CAKEFILES
CoffeeScript includes a (very) simple build system similar to Make and Rake.
Naturally, it’s called Cake, and is used for the tasks that build and test the
CoffeeScript language itself. Tasks are defined in a file named Cakefile, and
can be invoked by running cake [task] from within the directory. To print a list
of all the tasks and options, just type cake.
Task definitions are written in CoffeeScript, so you can put arbitrary code in
your Cakefile. Define a task with a name, a long description, and the function
to invoke when the task is run. If your task takes a command-line option, you
can define the option with short and long flags, and it will be made available
in the options object. Here’s a task that uses the Node.js API to rebuild
CoffeeScript’s parser:
fs = require 'fs' option '-o', '--output [DIR]', 'directory for compiled code'
task 'build:parser', 'rebuild the Jison parser', (options) -> require 'jison'
code = require('./lib/grammar').parser.generate() dir = options.output or 'lib'
fs.writeFile "#{dir}/parser.js", code
fs = require 'fs'
option '-o', '--output [DIR]', 'directory for compiled code'
task 'build:parser', 'rebuild the Jison parser', (options) ->
require 'jison'
code = require('./lib/grammar').parser.generate()
dir = options.output or 'lib'
fs.writeFile "#{dir}/parser.js", code
var fs; fs = require('fs'); option('-o', '--output [DIR]', 'directory for
compiled code'); task('build:parser', 'rebuild the Jison parser',
function(options) { var code, dir; require('jison'); code =
require('./lib/grammar').parser.generate(); dir = options.output || 'lib';
return fs.writeFile(`${dir}/parser.js`, code); });
var fs;
fs = require('fs');
option('-o', '--output [DIR]', 'directory for compiled code');
task('build:parser', 'rebuild the Jison parser', function(options) {
var code, dir;
require('jison');
code = require('./lib/grammar').parser.generate();
dir = options.output || 'lib';
return fs.writeFile(`${dir}/parser.js`, code);
});
If you need to invoke one task before another — for example, running build
before test, you can use the invoke function: invoke 'build'. Cake tasks are a
minimal way to expose your CoffeeScript functions to the command line, so don’t
expect any fanciness built-in. If you need dependencies, or async callbacks,
it’s best to put them in your code itself — not the cake task.
"TEXT/COFFEESCRIPT" SCRIPT TAGS
While it’s not recommended for serious use, CoffeeScripts may be included
directly within the browser using <script type="text/coffeescript"> tags. The
source includes a compressed and minified version of the compiler (Download
current version here, 77k when gzipped) as
docs/v2/browser-compiler-legacy/coffeescript.js. Include this file on a page
with inline CoffeeScript tags, and it will compile and evaluate them in order.
The usual caveats about CoffeeScript apply — your inline scripts will run within
a closure wrapper, so if you want to expose global variables or functions,
attach them to the window object.
INTEGRATIONS
CoffeeScript is part of the vast JavaScript ecosystem, and many libraries help
integrate CoffeeScript with JavaScript. Major projects, especially projects
updated to work with CoffeeScript 2, are listed here; more can be found in the
wiki pages. If there’s a project that you feel should be added to this section,
please open an issue or pull request. Projects are listed in alphabetical order
by category.
BUILD TOOLS
* Browserify with coffeeify
* Grunt with grunt-contrib-coffee
* Gulp with gulp-coffee
* Parcel with transformer-coffeescript
* Rollup with rollup-plugin-coffee-script
* Webpack with coffee-loader
CODE EDITORS
* Atom packages
* Sublime Text packages
* Visual Studio Code extensions
FRAMEWORKS
* Ember with ember-cli-coffeescript
* Meteor with coffeescript-compiler
LINTERS AND FORMATTING
* CoffeeLint
* ESLint with eslint-plugin-coffee
* Prettier with prettier-plugin-coffeescript
TESTING
* Jest with jest-preset-coffeescript
RESOURCES
* CoffeeScript on GitHub
* CoffeeScript Issues
Bug reports, feature proposals, and ideas for changes to the language belong
here.
* CoffeeScript Google Group
If you’d like to ask a question, the mailing list is a good place to get
help.
* The CoffeeScript Wiki
If you’ve ever learned a neat CoffeeScript tip or trick, or ran into a gotcha
— share it on the wiki.
* The FAQ
Perhaps your CoffeeScript-related question has been asked before. Check the
FAQ first.
* JS2Coffee
Is a very well done reverse JavaScript-to-CoffeeScript compiler. It’s not
going to be perfect (infer what your JavaScript classes are, when you need
bound functions, and so on…) — but it’s a great starting point for converting
simple scripts.
* High-Rez Logo
The CoffeeScript logo is available in SVG for use in presentations.
BOOKS
There are a number of excellent resources to help you get started with
CoffeeScript, some of which are freely available online.
* The Little Book on CoffeeScript is a brief 5-chapter introduction to
CoffeeScript, written with great clarity and precision by Alex MacCaw.
* Smooth CoffeeScript is a reimagination of the excellent book Eloquent
JavaScript, as if it had been written in CoffeeScript instead. Covers
language features as well as the functional and object oriented programming
styles. By E. Hoigaard.
* CoffeeScript: Accelerated JavaScript Development is Trevor Burnham’s thorough
introduction to the language. By the end of the book, you’ll have built a
fast-paced multiplayer word game, writing both the client-side and Node.js
portions in CoffeeScript.
* CoffeeScript Programming with jQuery, Rails, and Node.js is a new book by
Michael Erasmus that covers CoffeeScript with an eye towards real-world usage
both in the browser (jQuery) and on the server-side (Rails, Node).
* CoffeeScript Ristretto is a deep dive into CoffeeScript’s semantics from
simple functions up through closures, higher-order functions, objects,
classes, combinators, and decorators. By Reg Braithwaite.
* Testing with CoffeeScript is a succinct and freely downloadable guide to
building testable applications with CoffeeScript and Jasmine.
* CoffeeScript Application Development from Packt, introduces CoffeeScript
while walking through the process of building a demonstration web
application. A CoffeeScript Application Development Coookbook with over 90
“recipes” is also available.
* CoffeeScript in Action from Manning Publications, covers CoffeeScript syntax,
composition techniques and application development.
* CoffeeScript: Die Alternative zu JavaScript from dpunkt.verlag, is the first
CoffeeScript book in Deutsch.
SCREENCASTS
* A Sip of CoffeeScript is a Code School Course which combines 6 screencasts
with in-browser coding to make learning fun. The first level is free to try
out.
* Meet CoffeeScript is a 75-minute long screencast by PeepCode, now
PluralSight. Highly memorable for its animations which demonstrate
transforming CoffeeScript into the equivalent JS.
* If you’re looking for less of a time commitment, RailsCasts’ CoffeeScript
Basics should have you covered, hitting all of the important notes about
CoffeeScript in 11 minutes.
EXAMPLES
The best list of open-source CoffeeScript examples can be found on GitHub. But
just to throw out a few more:
* GitHub’s Hubot, a friendly IRC robot that can perform any number of useful
and useless tasks.
* sstephenson’s Pow, a zero-configuration Rack server, with comprehensive
annotated source.
* technoweenie’s Coffee-Resque, a port of Resque for Node.js.
* stephank’s Orona, a remake of the Bolo tank game for modern browsers.
* GitHub’s Atom, a hackable text editor built on web technologies.
* Basecamp’s Trix, a rich text editor for web apps.
WEB CHAT (IRC)
Quick help and advice can often be found in the CoffeeScript IRC room
#coffeescript on irc.freenode.net, which you can join via your web browser.
ANNOTATED SOURCE
You can browse the CoffeeScript 2.7.0 source in readable, annotated form here.
You can also jump directly to a particular source file:
* Grammar Rules — src/grammar
* Lexing Tokens — src/lexer
* The Rewriter — src/rewriter
* The Syntax Tree — src/nodes
* Lexical Scope — src/scope
* Helpers & Utility Functions — src/helpers
* The CoffeeScript Module — src/coffeescript
* Cake & Cakefiles — src/cake
* “coffee” Command-Line Utility — src/command
* Option Parsing — src/optparse
* Interactive REPL — src/repl
* Source Maps — src/sourcemap
CONTRIBUTING
Contributions are welcome! Feel free to fork the repo and submit a pull request.
Some features of ECMAScript are intentionally unsupported. Please review both
the open and closed issues on GitHub to see if the feature you’re looking for
has already been discussed. As a general rule, we don’t support ECMAScript
syntax for features that aren’t yet finalized (at Stage 4 in the proposal
approval process) or implemented in major browsers and/or Node (which can
sometimes happen for features in Stage 3). Any Stage 3 features that
CoffeeScript chooses to support should be considered experimental, subject to
breaking changes or removal until the feature reaches Stage 4.
For more resources on adding to CoffeeScript, please see the Wiki, especially
How The Parser Works.
There are several things you can do to increase your odds of having your pull
request accepted:
* Create tests! Any pull request should probably include basic tests to verify
you didn’t break anything, or future changes won’t break your code.
* Follow the style of the rest of the CoffeeScript codebase.
* Ensure any ECMAScript syntax is mature (at Stage 4, or at Stage 3 with
support in major browsers or runtimes).
* Add only features that have broad utility, rather than a feature aimed at a
specific use case or framework.
Of course, it’s entirely possible that you have a great addition, but it doesn’t
fit within these constraints. Feel free to roll your own solution; you will have
plenty of company.
UNSUPPORTED ECMASCRIPT FEATURES
There are a few ECMAScript features that CoffeeScript intentionally doesn’t
support.
LET AND CONST: BLOCK-SCOPED AND REASSIGNMENT-PROTECTED VARIABLES
When CoffeeScript was designed, var was intentionally omitted. This was to spare
developers the mental housekeeping of needing to worry about variable
declaration (var foo) as opposed to variable assignment (foo = 1). The
CoffeeScript compiler automatically takes care of declaration for you, by
generating var statements at the top of every function scope. This makes it
impossible to accidentally declare a global variable.
let and const add a useful ability to JavaScript in that you can use them to
declare variables within a block scope, for example within an if statement body
or a for loop body, whereas var always declares variables in the scope of an
entire function. When CoffeeScript 2 was designed, there was much discussion of
whether this functionality was useful enough to outweigh the simplicity offered
by never needing to consider variable declaration in CoffeeScript. In the end,
it was decided that the simplicity was more valued. In CoffeeScript there
remains only one type of variable.
Keep in mind that const only protects you from reassigning a variable; it
doesn’t prevent the variable’s value from changing, the way constants usually do
in other languages:
> const obj = {foo: 'bar'};
> obj.foo = 'baz'; // Allowed!
> obj = {}; // Throws error
NAMED FUNCTIONS AND FUNCTION DECLARATIONS
Newcomers to CoffeeScript often wonder how to generate the JavaScript function
foo() {}, as opposed to the foo = function() {} that CoffeeScript produces. The
first form is a function declaration, and the second is a function expression.
As stated above, in CoffeeScript everything is an expression, so naturally we
favor the expression form. Supporting only one variant helps avoid confusing
bugs that can arise from the subtle differences between the two forms.
Technically, foo = function() {} is creating an anonymous function that gets
assigned to a variable named foo. Some very early versions of CoffeeScript named
this function, e.g. foo = function foo() {}, but this was dropped because of
compatibility issues with Internet Explorer. For a while this annoyed people, as
these functions would be unnamed in stack traces; but modern JavaScript runtimes
infer the names of such anonymous functions from the names of the variables to
which they’re assigned. Given that this is the case, it’s simplest to just
preserve the current behavior.
GET AND SET KEYWORD SHORTHAND SYNTAX
get and set, as keywords preceding functions or class methods, are intentionally
unimplemented in CoffeeScript.
This is to avoid grammatical ambiguity, since in CoffeeScript such a construct
looks identical to a function call (e.g. get(function foo() {})); and because
there is an alternate syntax that is slightly more verbose but just as
effective:
screen = width: 1200 ratio: 16/9 Object.defineProperty screen, 'height', get: ->
this.width / this.ratio set: (val) -> this.width = val * this.ratio
screen =
width: 1200
ratio: 16/9
Object.defineProperty screen, 'height',
get: ->
this.width / this.ratio
set: (val) ->
this.width = val * this.ratio
var screen; screen = { width: 1200, ratio: 16 / 9 };
Object.defineProperty(screen, 'height', { get: function() { return this.width /
this.ratio; }, set: function(val) { return this.width = val * this.ratio; } });
var screen;
screen = {
width: 1200,
ratio: 16 / 9
};
Object.defineProperty(screen, 'height', {
get: function() {
return this.width / this.ratio;
},
set: function(val) {
return this.width = val * this.ratio;
}
});
screen.height
BREAKING CHANGES FROM COFFEESCRIPT 1.X TO 2
CoffeeScript 2 aims to output as much idiomatic ES2015+ syntax as possible with
as few breaking changes from CoffeeScript 1.x as possible. Some breaking
changes, unfortunately, were unavoidable.
BOUND (FAT ARROW) FUNCTIONS
In CoffeeScript 1.x, => compiled to a regular function but with references to
this/@ rewritten to use the outer scope’s this, or with the inner function bound
to the outer scope via .bind (hence the name “bound function”). In CoffeeScript
2, => compiles to ES2015’s =>, which behaves slightly differently. The largest
difference is that in ES2015, => functions lack an arguments object:
outer = -> inner = => Array.from arguments inner() outer(1, 2) # Returns '' in
CoffeeScript 1.x, '1, 2' in CoffeeScript 2
outer = ->
inner = => Array.from arguments
inner()
outer(1, 2) # Returns '' in CoffeeScript 1.x, '1, 2' in CoffeeScript 2
var outer; outer = function() { var inner; inner = () => { return
Array.from(arguments); }; return inner(); }; outer(1, 2); // Returns '' in
CoffeeScript 1.x, '1, 2' in CoffeeScript 2
var outer;
outer = function() {
var inner;
inner = () => {
return Array.from(arguments);
};
return inner();
};
outer(1, 2); // Returns '' in CoffeeScript 1.x, '1, 2' in CoffeeScript 2
outer(1, 2)
DEFAULT VALUES FOR FUNCTION PARAMETERS AND DESTRUCTURED ELEMENTS
Per the ES2015 spec regarding function default parameters and destructuring
default values, default values are only applied when a value is missing or
undefined. In CoffeeScript 1.x, the default value would be applied in those
cases but also if the value was null.
f = (a = 1) -> a f(null) # Returns 1 in CoffeeScript 1.x, null in CoffeeScript 2
f = (a = 1) -> a
f(null) # Returns 1 in CoffeeScript 1.x, null in CoffeeScript 2
var f; f = function(a = 1) { return a; }; f(null); // Returns 1 in CoffeeScript
1.x, null in CoffeeScript 2
var f;
f = function(a = 1) {
return a;
};
f(null); // Returns 1 in CoffeeScript 1.x, null in CoffeeScript 2
f(null)
{a = 1} = {a: null} a # Equals 1 in CoffeeScript 1.x, null in CoffeeScript 2
{a = 1} = {a: null}
a # Equals 1 in CoffeeScript 1.x, null in CoffeeScript 2
var a; ({a = 1} = { a: null }); a; // Equals 1 in CoffeeScript 1.x, null in
CoffeeScript 2
var a;
({a = 1} = {
a: null
});
a; // Equals 1 in CoffeeScript 1.x, null in CoffeeScript 2
a
BOUND GENERATOR FUNCTIONS
Bound generator functions, a.k.a. generator arrow functions, aren’t allowed in
ECMAScript. You can write function* or =>, but not both. Therefore, CoffeeScript
code like this:
> f = => yield this
> # Throws a compiler error
Needs to be rewritten the old-fashioned way:
self = this f = -> yield self
self = this
f = -> yield self
var f, self; self = this; f = function*() { return (yield self); };
var f, self;
self = this;
f = function*() {
return (yield self);
};
CLASSES ARE COMPILED TO ES2015 CLASSES
ES2015 classes and their methods have some restrictions beyond those on regular
functions.
Class constructors can’t be invoked without new:
> (class)()
> # Throws a TypeError at runtime
ES2015 classes don’t allow bound (fat arrow) methods. The CoffeeScript compiler
goes through some contortions to preserve support for them, but one thing that
can’t be accommodated is calling a bound method before it is bound:
> class Base
> constructor: ->
> @onClick() # This works
> clickHandler = @onClick
> clickHandler() # This throws a runtime error
>
> class Component extends Base
> onClick: =>
> console.log 'Clicked!', @
Class methods can’t be used with new (uncommon):
> class Namespace
> @Klass = ->
> new Namespace.Klass # Throws a TypeError at runtime
Due to the hoisting required to compile to ES2015 classes, dynamic keys in class
methods can’t use values from the executable class body unless the methods are
assigned in prototype style.
> class A
> name = 'method'
> "#{name}": -> # This method will be named 'undefined'
> @::[name] = -> # This will work; assigns to `A.prototype.method`
SUPER AND THIS
In the constructor of a derived class (a class that extends another class), this
cannot be used before calling super:
> class B extends A
> constructor: -> this # Throws a compiler error
This also means you cannot pass a reference to this as an argument to super in
the constructor of a derived class:
> class B extends A
> constructor: (@arg) ->
> super @arg # Throws a compiler error
This is a limitation of ES2015 classes. As a workaround, assign to this after
the super call:
class B extends A constructor: (arg) -> super arg @arg = arg
class B extends A
constructor: (arg) ->
super arg
@arg = arg
var B; B = class B extends A { constructor(arg) { super(arg); this.arg = arg; }
};
var B;
B = class B extends A {
constructor(arg) {
super(arg);
this.arg = arg;
}
};
SUPER AND EXTENDS
Due to a syntax clash with super with accessors, “bare” super (the keyword super
without parentheses) no longer compiles to a super call forwarding all
arguments.
> class B extends A
> foo: -> super
> # Throws a compiler error
Arguments can be forwarded explicitly using splats:
class B extends A foo: -> super arguments...
class B extends A
foo: -> super arguments...
var B; B = class B extends A { foo() { return super.foo(...arguments); } };
var B;
B = class B extends A {
foo() {
return super.foo(...arguments);
}
};
Or if you know that the parent function doesn’t require arguments, just call
super():
class B extends A foo: -> super()
class B extends A
foo: -> super()
var B; B = class B extends A { foo() { return super.foo(); } };
var B;
B = class B extends A {
foo() {
return super.foo();
}
};
CoffeeScript 1.x allowed the extends keyword to set up prototypal inheritance
between functions, and super could be used manually prototype-assigned
functions:
> A = ->
> B = ->
> B extends A
> B.prototype.foo = -> super arguments...
> # Last two lines each throw compiler errors in CoffeeScript 2
Due to the switch to ES2015 extends and super, using these keywords for
prototypal functions are no longer supported. The above case could be refactored
to:
# Helper functions hasProp = {}.hasOwnProperty extend = (child, parent) -> ctor
= -> @constructor = child return for key of parent if hasProp.call(parent, key)
child[key] = parent[key] ctor.prototype = parent.prototype child.prototype = new
ctor child A = -> B = -> extend B, A B.prototype.foo = -> A::foo.apply this,
arguments
# Helper functions
hasProp = {}.hasOwnProperty
extend = (child, parent) ->
ctor = ->
@constructor = child
return
for key of parent
if hasProp.call(parent, key)
child[key] = parent[key]
ctor.prototype = parent.prototype
child.prototype = new ctor
child
A = ->
B = ->
extend B, A
B.prototype.foo = -> A::foo.apply this, arguments
// Helper functions var A, B, extend, hasProp; hasProp = {}.hasOwnProperty;
extend = function(child, parent) { var ctor, key; ctor = function() {
this.constructor = child; }; for (key in parent) { if (hasProp.call(parent,
key)) { child[key] = parent[key]; } } ctor.prototype = parent.prototype;
child.prototype = new ctor(); return child; }; A = function() {}; B = function()
{}; extend(B, A); B.prototype.foo = function() { return
A.prototype.foo.apply(this, arguments); };
// Helper functions
var A, B, extend, hasProp;
hasProp = {}.hasOwnProperty;
extend = function(child, parent) {
var ctor, key;
ctor = function() {
this.constructor = child;
};
for (key in parent) {
if (hasProp.call(parent, key)) {
child[key] = parent[key];
}
}
ctor.prototype = parent.prototype;
child.prototype = new ctor();
return child;
};
A = function() {};
B = function() {};
extend(B, A);
B.prototype.foo = function() {
return A.prototype.foo.apply(this, arguments);
};
or
class A class B extends A foo: -> super arguments...
class A
class B extends A
foo: -> super arguments...
var A, B; A = class A {}; B = class B extends A { foo() { return
super.foo(...arguments); } };
var A, B;
A = class A {};
B = class B extends A {
foo() {
return super.foo(...arguments);
}
};
JSX AND THE < AND > OPERATORS
With the addition of JSX, the < and > characters serve as both the “less than”
and “greater than” operators and as the delimiters for XML tags, like <div>. For
best results, in general you should always wrap the operators in spaces to
distinguish them from XML tags: i < len, not i<len. The compiler tries to be
forgiving when it can be sure what you intend, but always putting spaces around
the “less than” and “greater than” operators will remove ambiguity.
LITERATE COFFEESCRIPT PARSING
CoffeeScript 2’s parsing of Literate CoffeeScript has been refactored to now be
more careful about not treating indented lists as code blocks; but this means
that all code blocks (unless they are to be interpreted as comments) must be
separated by at least one blank line from lists.
Code blocks should also now maintain a consistent indentation level—so an
indentation of one tab (or whatever you consider to be a tab stop, like 2 spaces
or 4 spaces) should be treated as your code’s “left margin,” with all code in
the file relative to that column.
Code blocks that you want to be part of the commentary, and not executed, must
have at least one line (ideally the first line of the block) completely
unindented.
ARGUMENT PARSING AND SHEBANG (#!) LINES
In CoffeeScript 1.x, -- was required after the path and filename of the script
to be run, but before any arguments passed to that script. This convention is
now deprecated. So instead of:
> coffee [options] path/to/script.coffee -- [args]
Now you would just type:
> coffee [options] path/to/script.coffee [args]
The deprecated version will still work, but it will print a warning before
running the script.
On non-Windows platforms, a .coffee file can be made executable by adding a
shebang (#!) line at the top of the file and marking the file as executable. For
example:
> #!/usr/bin/env coffee
>
> x = 2 + 2
> console.log x
If this were saved as executable.coffee, it could be made executable and run:
> ▶ chmod +x ./executable.coffee
> ▶ ./executable.coffee
> 4
In CoffeeScript 1.x, this used to fail when trying to pass arguments to the
script. Some users on OS X worked around the problem by using #!/usr/bin/env
coffee -- as the first line of the file. That didn’t work on Linux, however,
which cannot parse shebang lines with more than a single argument. While such
scripts will still run on OS X, CoffeeScript will now display a warning before
compiling or evaluating files that begin with a too-long shebang line. Now that
CoffeeScript 2 supports passing arguments without needing --, we recommend
simply changing the shebang lines in such scripts to just #!/usr/bin/env coffee.
CHANGELOG
2.7.0 — APRIL 22, 2022
* The import assertions syntax is now supported. This allows statements like
export { version } from './package.json' assert { type: 'json' } or
expressions like import('./calendar.json', { assert { type: 'json' } }).
* CoffeeScript no longer always patches Node’s error stack traces. This
patching, where the line and column numbers are adjusted to match the source
CoffeeScript rather than the generated JavaScript, caused conflicts with
other libraries and is unnecessary when Node’s new --enable-source-maps flag
is passed. The patching will now occur only when --enable-source-maps is not
set, no other library has already patched the stack traces, and
require('coffeescript/register') is used. The patching can be enabled
explicitly via require('coffeescript').patchStackTrace() or import {
patchStackTrace } from 'coffeescript'; patchStackTrace().
* Bugfix for an issue where block (triple-quoted) strings weren’t getting
transpiled correctly into a JSX expression container wrapping the template
literal (such as <div a={`...`} />).
* Bugfixes for line continuations not behaving as expected for a nonempty first
line of an explicit [ array or { object literal.
2.6.1 — OCTOBER 2, 2021
* The coffeescript package itself now supports named exports when used by ES
modules in Node.js; or in other words, import { compile } from 'coffeescript'
now works, rather than only import CoffeeScript from 'coffeescript'.
* Bugfix for a stack overflow error when compiling large files in non-bare
mode.
2.6.0 — SEPTEMBER 18, 2021
* The syntax import.meta, including import.meta.url, is now supported.
* The await keyword is now supported outside of functions (in other words, at
the top level). Note that JavaScript runtimes only support this for ES
modules.
* Bugfix for a for comprehension at the end of an unless or until line.
2.5.1 — JANUARY 30, 2020
* Object splats can now include prototype shorthands, such as a = {b::c...};
and soaks, such as a = {b?.c..., d?()...}.
* Bugfix for regression in 2.5.0 where compilation became much slower for files
with Windows-style line endings.
* Bugfix for an implicit object after a line continuation keyword like or
inside a larger implicit object.
2.5.0 — DECEMBER 30, 2019
* The compiler now supports a new ast option, available via --ast on the
command line or ast via the Node API. This option outputs an “abstract syntax
tree,” or a JSON-like representation of the input CoffeeScript source code.
This AST follows Babel’s spec as closely as possible, for compatibility with
tools that work with JavaScript source code. Two tools that use this new AST
output are eslint-plugin-coffee, a plugin to lint CoffeeScript via ESLint;
and prettier-plugin-coffeescript, a plugin to reformat CoffeeScript source
code via Prettier. The structure and properties of CoffeeScript’s AST are not
final and may undergo breaking changes between CoffeeScript versions; please
open an issue if you are interested in creating new integrations.
* Numeric separators are now supported in CoffeeScript, following the same
syntax as JavaScript: 1_234_567.
* BigInt numbers are now supported in CoffeeScript, following the same syntax
as JavaScript: 42n.
* ''' and """ strings are now output as more readable JavaScript template
literals, or backtick (`) strings, with actual newlines rather than \n escape
sequences.
* Classes can now contain computed properties, e.g. [someVar]: -> or
@[anotherVar]: ->.
* JSX tags can now contain XML-style namespaces, e.g. <image
xlink:href="data:image/png" /> or <Something:Tag></Something:Tag>.
* Bugfixes for comments after colons not appearing the output; reserved words
mistakenly being disallowed as JSX attributes; indented leading elisions in
multiline arrays; and invalid location data in source maps.
2.4.1 — APRIL 7, 2019
* Both the traditional ES5 and modern ES module versions of the CoffeeScript
browser compiler are now published to NPM, enabling the browser compilers’
use via services that provide NPM modules’ code available via public CDN. The
traditional version is referenced via the package.json "browser" field, and
the ES module version via the "module" field.
2.4.0 — MARCH 28, 2019
* Dynamic import() expressions are now supported. The parentheses are always
required, to distinguish from import statements. See Modules. Note that as of
this writing, the JavaScript feature itself is still Stage 3; if it changes
before being fully standardized, it may change in CoffeeScript too. Using
import() before its upstream ECMAScript proposal is finalized should be
considered provisional, subject to breaking changes if the proposal changes
or is rejected. We have also revised our policy on Stage 3 ECMAScript
features, to support them when the features are shipped in significant
runtimes such as major browsers or Node.js.
* There are now two browser versions of the CoffeeScript compiler: the
traditional one that’s been published for years, and a new ES module version
that can be used via import. If your browser supports it, it is in effect on
this page. A reference to the ES module browser compiler is in the
package.json "module" field.
* The Node API now exposes the previously private registerCompiled method, to
allow plugins that use the coffeescript package to take advantage of
CoffeeScript’s internal caching.
* Bugfixes for commas in strings in block arrays, a reference to @ not being
maintained in a do block in a class, and function default parameters should
no longer be wrapped by extraneous parentheses.
2.3.2 — SEPTEMBER 18, 2018
* Babel 7 is now supported. With version 7, the Babel team moved from
babel-core on NPM to @babel/core. Now the CoffeeScript --transpile option
will first search for @babel/core (Babel versions 7 and above) and then
search for babel-core (versions 6 and below) to try to find an installed
version of Babel to use for transpilation.
* The syntax new.target is now supported.
* You can now follow the keyword yield with an indented object, like has
already been allowed for return and other keywords.
* Previously, any comments inside a JSX tag or attribute would cause
interpolation braces ({ and }) to be output. This is only necessary for line
(#, or // in JavaScript) comments, not here (###, or /* */) comments; so now
the compiler checks if all the comments that would trigger the braces are
here comments, and if so it doesn’t generate the unnecessary interpolation
braces.
2.3.1 — MAY 20, 2018
* Returning a JSX tag that is adjacent to another JSX tag, as opposed to
returning a root JSX tag or fragment, is invalid JSX syntax. Babel throws an
error on this, and now the CoffeeScript compiler does too.
* Invalid indentation inside a JSX interpolation (the middle of <tag>{ ...
}</tag>) now throws an error.
* The browser compiler, used in Try CoffeeScript and similar web-based
CoffeeScript editors, now evaluates code in a global scope rather than the
scope of the browser compiler. This improves performance of code executed via
the browser compiler.
* Syntax cleanup: it is now possible for an implicit function call to take a
body-less class as an argument, and ?:: now behaves identically to :: with
regard to implying a line continuation.
2.3.0 — APRIL 28, 2018
* This release adds support for all the new features and syntaxes in ES2018
that weren’t already possible in CoffeeScript. For all of the below features,
make sure that you transpile unless you know that your target runtime(s)
support each feature.
* Asynchronous iterators are now supported. You can now yield an await call,
e.g. do -> until file.EOF then yield await file.readLine().
* Object splats/destructuring, a.k.a. object rest/spread syntax, has been
standardized as part of ES2018 and therefore this release removes the
polyfill that had previously been supporting this syntax. Code like {a, b,
rest...} = obj now outputs more or less just like it appears, rather than
being converted into an Object.assign call. Note that there are some subtle
differences between the Object.assign polyfill and the native implementation.
* The exponentiation operator, **, and exponentiation assignment operator **=
are new to JavaScript in ES2018. Now code like a ** 3 is output as it
appears, rather than being converted into Math.pow(a, 3) as it was before.
* The s (dotAll) flag is now supported in regular expressions.
2.2.4 — MARCH 28, 2018
* When the by value in a for loop is a literal number, e.g. for x in [2..1] by
-1, fewer checks are necessary to determine if the loop is in range.
* Bugfix for regression in 2.2.0 where a statement inside parentheses, e.g.
(fn(); break) while condition, was compiling. Pure statements like break or
return cannot turn a parenthesized block into an expression, and should throw
an error.
2.2.3 — MARCH 10, 2018
* Bugfix for object destructuring with an empty array as a key’s value: { key:
[] } = obj.
* Bugfix for array destructuring onto targets attached to this: [ @most... ,
@penultimate, @last ] = arr.
2.2.2 — FEBRUARY 20, 2018
* Bugfix for regression in 2.2.0 where a range with a by (step) value that
increments or decrements in the opposite direction as the range was returning
an array containing the first value of the range, whereas it should be
returning an empty array. In other words, x for x in [2..1] by 1 should equal
[], not [2] (because the step value is positive 1, counting up, whereas the
range goes from 2 to 1, counting down).
* Bugfixes for allowing backslashes in import and export statements and lines
that trigger the start of an indented block, like an if statement.
2.2.1 — FEBRUARY 5, 2018
* Bugfix for regression in 2.2.0 involving an error thrown by the compiler in
certain cases when using destructuring with a splat or expansion in an array.
* Bugfix for regression in 2.2.0 where in certain cases a range iterator
variable was declared in the global scope.
2.2.0 — JANUARY 31, 2018
* This release fixes all currently open bugs, dating as far back as 2014, 2012
and 2011.
* Potential breaking change: An inline if or switch statement with an ambiguous
else, such as if no then if yes then alert 1 else alert 2, now compiles where
the else always corresponds to the closest open then. Previously the behavior
of an ambiguous else was unpredictable. If your code has any if … then or
switch … then statements with multiple thens (and one or more elses) the
compiled output might be different now, unless you had resolved ambiguity via
parentheses. We made this change because the previous behavior was
inconsistent and basically a bug: depending on what grammar was where, for
example if there was an inline function or something that implied a block,
the else might bind to an earlier then rather than a later then. Now an else
essentially closes a block opened by a then, similar to closing an open
parenthesis.
* When a required then is missing, the error more accurately points out the
location of the mistake.
* An error is thrown when the coffee command is run in an environment that
doesn’t support some ES2015 JavaScript features that the CoffeeScript
compiler itself requires. This can happen if CoffeeScript is installed in
Node older than version 6.
* Destructuring with a non-final splat/spread, e.g. [open, contents..., close]
= tag.split('') is now output using ES2015 rest syntax.
* Functions named get or set can be used without parentheses in more cases,
including when attached to this or @ or ?.; or when the first argument is an
implicit object, e.g. @set key: 'val'.
* Statements such as break can now be used inside parentheses, e.g.
(doSomething(); break) while condition or (pick(key); break) for key of obj.
* Bugfix for assigning to a property attached to this/@ in destructuring, e.g.
({@prop = yes, @otherProp = no}) ->.
* Bugfix for incorrect errors being thrown about calling super with a parameter
attached to this when said parameter is in a lower scope, e.g. class Child
extends Parent then constructor: -> super(-> @prop).
* Bugfix to prevent a possible infinite loop when a for loop is given a
variable to step by, e.g. for x in [1..3] by step (as opposed to by 0.5 or
some other primitive numeric value).
* Bugfix to no longer declare iterator variables twice when evaluating a range,
e.g. end = 3; fn [0..end].
* Bugfix for incorrect scope of variables in chained calls, e.g. start(x =
3).then(-> x = 4).
* Bugfix for incorrect scope of variables in a function passed to do, e.g. for
[1..3] then masked = 10; do -> alert masked.
* Bugfix to no longer throw a syntax error for a trailing comma in a function
call, e.g. fn arg1, arg2,.
* Bugfix for an expression in a property access, e.g. a[!b in c..].
* Bugfix to allow a line continuation backslash (\) at any point in a for line.
2.1.1 — DECEMBER 28, 2017
* Bugfix to set the correct context for executable class bodies. So in class @B
extends @A then @property = 1, the @ in @property now refers to the class,
not the global object.
* Bugfix where anonymous classes were getting created using the same automatic
variable name. They now each receive unique names, so as not to override each
other.
2.1.0 — DECEMBER 9, 2017
* Computed property keys in object literals are now supported: obj = { ['key' +
i]: 42 }, or obj = [Symbol.iterator]: -> yield i++.
* Skipping of array elements, a.k.a. elision, is now supported: arr = [a, , b],
or [, protocol] = url.match /^(.*):\/\//.
* JSX fragments syntax is now supported.
* Bugfix where /// within a # line comment inside a /// block regex was
erroneously closing the regex, rather than being treated as part of the
comment.
* Bugfix for incorrect output for object rest destructuring inside array
destructuring.
2.0.3 — NOVEMBER 25, 2017
* Bugfix for export default followed by an implicit object that contains an
explicit object, for example exportedMember: { obj... }.
* Bugfix for key, val of obj after an implicit object member, e.g. foo: bar for
key, val of obj.
* Bugfix for combining array and object destructuring, e.g. [ ..., {a, b} ] =
arr.
* Bugfix for an edge case where it was possible to create a bound (=>)
generator function, which should throw an error as such functions aren’t
allowed in ES2015.
* Bugfix for source maps: .map files should always have the same base filename
as the requested output filename. So coffee --map --output foo.js test.coffee
should generate foo.js and foo.js.map.
* Bugfix for incorrect source maps generated when using --transpile with --map
for multiple input files.
* Bugfix for comments at the beginning or end of input into the REPL (coffee
--interactive).
2.0.2 — OCTOBER 25, 2017
* --transpile now also applies to required or imported CoffeeScript files.
* --transpile can be used with the REPL: coffee --interactive --transpile.
* Improvements to comments output that should now cover all of the Flow
comment-based syntax. Inline ### comments near variable initial assignments
are now output in the variable declaration statement, and ### comments near a
class and method names are now output where Flow expects them.
* Importing CoffeeScript keywords is now allowed, so long as they’re aliased:
import { and as andFn } from 'lib'. (You could also do import lib from 'lib'
and then reference lib.and.)
* Calls to functions named get and set no longer throw an error when given a
bracketless object literal as an argument: obj.set propertyName:
propertyValue.
* In the constructor of a derived class (a class that extends another class),
you cannot call super with an argument that references this: class Child
extends Parent then constructor: (@arg) -> super(@arg). This isn’t allowed in
JavaScript, and now the CoffeeScript compiler will throw an error. Instead,
assign to this after calling super: (arg) -> super(arg); @arg = arg.
* Bugfix for incorrect output when backticked statements and hoisted
expressions were both in the same class body. This allows a backticked line
like `field = 3`, for people using the experimental class fields syntax, in
the same class along with traditional class body expressions like prop: 3
that CoffeeScript outputs as part of the class prototype.
* Bugfix for comments not output before a complex ? operation, e.g. @a ? b.
* All tests now pass in Windows.
2.0.1 — SEPTEMBER 25, 2017
* babel-core is no longer listed in package.json, even as an
optionalDependency, to avoid it being automatically installed for most users.
If you wish to use --transpile, simply install babel-core manually. See
Transpilation.
* --transpile now relies on Babel to find its options, i.e. the .babelrc file
in the path of the file(s) being compiled. (Previously the CoffeeScript
compiler was duplicating this logic, so nothing has changed from a user’s
perspective.) This provides automatic support for additional ways to pass
options to Babel in future versions, such as the .babelrc.js file coming in
Babel 7.
* Backticked expressions in a class body, outside any class methods, are now
output in the JavaScript class body itself. This allows for passing through
experimental JavaScript syntax like the class fields proposal, assuming your
transpiler supports it.
2.0.0 — SEPTEMBER 17, 2017
* Added --transpile flag or transpile Node API option to tell the CoffeeScript
compiler to pipe its output through Babel before saving or returning it; see
Transpilation. Also changed the -t short flag to refer to --transpile instead
of --tokens.
* Always populate source maps’ sourcesContent property.
* Bugfixes for destructuring and for comments in JSX.
* Note that these are only the changes between 2.0.0-beta5 and 2.0.0. See below
for all changes since 1.x.
2.0.0-BETA5 — SEPTEMBER 1, 2017
* Node 6 is now supported, and we will try to maintain that as the minimum
required version for CoffeeScript 2 via the coffee command or Node API. Older
versions of Node, or non-evergreen browsers, can compile via the legacy
browser compiler.
* The command line --output flag now allows you to specify an output filename,
not just an output folder.
* The command line --require flag now properly handles filenames or module
names that are invalid identifiers (like an NPM module with a hyphen in the
name).
* Object.assign, output when object destructuring is used, is polyfilled using
the same polyfill that Babel outputs. This means that polyfills shouldn’t be
required unless support for Internet Explorer 8 or below is desired (or your
own code uses a feature that requires a polyfill). See ES2015+ Output.
* A string or JSX interpolation that contains only a comment ("a#{### comment
###}b" or <div>{### comment ###}</div>) is now output (`a${/* comment */}b`)
* Interpolated strings (ES2015 template literals) that contain quotation marks
no longer have the quotation marks escaped: `say "${message}"`
* It is now possible to chain after a function literal (for example, to define
a function and then call .call on it).
* The results of the async tests are included in the output when you run cake
test.
* Bugfixes for object destructuring; expansions in function parameters;
generated reference variables in function parameters; chained functions after
do; splats after existential operator soaks in arrays ([a?.b...]); trailing
if with splat in arrays or function parameters ([a if b...]); attempting to
throw an if, for, switch, while or other invalid construct.
* Bugfixes for syntactical edge cases: semicolons after = and other
“mid-expression” tokens; spaces after ::; and scripts that begin with : or *.
* Bugfixes for source maps generated via the Node API; and stack trace line
numbers when compiling CoffeeScript via the Node API from within a .coffee
file.
2.0.0-BETA4 — AUGUST 2, 2017
* This release includes all the changes from 1.12.6 to 1.12.7.
* Line comments (starting with #) are now output in the generated JavaScript.
* Block comments (delimited by ###) are now allowed anywhere, including inline
where they previously weren’t possible. This provides support for static type
annotations using Flow’s comments-based syntax.
* Spread syntax (... for objects) is now supported in JSX tags: <div {props...}
/>.
* Argument parsing for scripts run via coffee is improved. See breaking
changes.
* CLI: Propagate SIGINT and SIGTERM signals when node is forked.
* await in the REPL is now allowed without requiring a wrapper function.
* do super is now allowed, and other accesses of super like super.x.y or
super['x'].y now work.
* Splat/spread syntax triple dots are now allowed on either the left or the
right (so props... or ...props are both valid).
* Tagged template literals are recognized as callable functions.
* Bugfixes for object spread syntax in nested properties.
* Bugfixes for destructured function parameter default values.
2.0.0-BETA3 — JUNE 29, 2017
* JSX is now supported.
* Object rest/spread properties are now supported.
* Bound (fat arrow) methods are once again supported in classes; though an
error will be thrown if you attempt to call the method before it is bound.
See breaking changes for classes.
* The REPL no longer warns about assigning to _.
* Bugfixes for destructured nested default values and issues related to
chaining or continuing expressions across multiple lines.
2.0.0-BETA2 — MAY 15, 2017
* This release includes all the changes from 1.12.5 to 1.12.6.
* Bound (fat arrow) methods in classes must be declared in the class
constructor, after super() if the class is extending a parent class. See
breaking changes for classes.
* All unnecessary utility helper functions have been removed, including the
polyfills for indexOf and bind.
* The extends keyword now only works in the context of classes; it cannot be
used to extend a function prototype. See breaking changes for extends.
* Literate CoffeeScript is now parsed entirely based on indentation, similar to
the 1.x implementation; there is no longer a dependency for parsing Markdown.
See breaking changes for Literate CoffeeScript parsing.
* JavaScript reserved words used as properties are no longer wrapped in quotes.
* require('coffeescript') should now work in non-Node environments such as the
builds created by Webpack or Browserify. This provides a more convenient way
to include the browser compiler in builds intending to run in a browser
environment.
* Unreachable break statements are no longer added after switch cases that
throw exceptions.
* The browser compiler is now compiled using Babili and transpiled down to
Babel’s env preset (should be safe for use in all browsers in current use,
not just evergreen versions).
* Calling functions @get or @set no longer throws an error about required
parentheses. (Bare get or set, not attached to an object or @, still
intentionally throws a compiler error.)
* If $XDG_CACHE_HOME is set, the REPL .coffee_history file is saved there.
2.0.0-BETA1 — APRIL 13, 2017
* Initial beta release of CoffeeScript 2. No further breaking changes are
anticipated.
* Destructured objects and arrays now output using ES2015+ syntax whenever
possible.
* Literate CoffeeScript now has much better support for parsing Markdown,
thanks to using Markdown-It to detect Markdown sections rather than just
looking at indentation.
* Calling a function named get or set now requires parentheses, to disambiguate
from the get or set keywords (which are disallowed).
* The compiler now requires Node 7.6+, the first version of Node to support
asynchronous functions without requiring a flag.
2.0.0-ALPHA1 — FEBRUARY 20, 2017
* Initial alpha release of CoffeeScript 2. The CoffeeScript compiler now
outputs ES2015+ syntax whenever possible. See breaking changes.
* Classes are output using ES2015 class and extends keywords.
* Added support for async/await.
* Bound (arrow) functions now output as => functions.
* Function parameters with default values now use ES2015 default values syntax.
* Splat function parameters now use ES2015 spread syntax.
* Computed properties now use ES2015 syntax.
* Interpolated strings (template literals) now use ES2015 backtick syntax.
* Improved support for recognizing Markdown in Literate CoffeeScript files.
* Mixing tabs and spaces in indentation is now disallowed.
* Browser compiler is now minified using the Google Closure Compiler
(JavaScript version).
* Node 7+ required for CoffeeScript 2.
1.12.7 — JULY 15, 2017
* Fix regressions in 1.12.6 related to chained function calls and indented
return and throw arguments.
* The REPL no longer warns about assigning to _.
1.12.6 — MAY 14, 2017
* The return and export keywords can now accept implicit objects (defined by
indentation, without needing braces).
* Support Unicode code point escapes (e.g. \u{1F4A9}).
* The coffee command now first looks to see if CoffeeScript is installed under
node_modules in the current folder, and executes the coffee binary there if
so; or otherwise it runs the globally installed one. This allows you to have
one version of CoffeeScript installed globally and a different one installed
locally for a particular project. (Likewise for the cake command.)
* Bugfixes for chained function calls not closing implicit objects or
ternaries.
* Bugfixes for incorrect code generated by the ? operator within a termary if
statement.
* Fixed some tests, and failing tests now result in a nonzero exit code.
1.12.5 — APRIL 9, 2017
* Better handling of default, from, as and * within import and export
statements. You can now import or export a member named default and the
compiler won’t interpret it as the default keyword.
* Fixed a bug where invalid octal escape sequences weren’t throwing errors in
the compiler.
1.12.4 — FEBRUARY 17, 2017
* The cake commands have been updated, with new watch options for most tasks.
Clone the CoffeeScript repo and run cake at the root of the repo to see the
options.
* Fixed a bug where exporting a referenced variable was preventing the variable
from being declared.
* Fixed a bug where the coffee command wasn’t working for a .litcoffee file.
* Bugfixes related to tokens and location data, for better source maps and
improved compatibility with downstream tools.
1.12.3 — JANUARY 23, 2017
* @ values can now be used as indices in for expressions. This loosens the
compilation of for expressions to allow the index variable to be an @ value,
e.g. do @visit for @node, @index in nodes. Within @visit, the index of the
current node (@node) would be available as @index.
* CoffeeScript’s patched Error.prepareStackTrace has been restored, with some
revisions that should prevent the erroneous exceptions that were making life
difficult for some downstream projects. This fixes the incorrect line numbers
in stack traces since 1.12.2.
* The //= operator’s output now wraps parentheses around the right operand,
like the other assignment operators.
1.12.2 — DECEMBER 15, 2016
* The browser compiler can once again be built unminified via MINIFY=false cake
build:browser.
* The error-prone patched version of Error.prepareStackTrace has been removed.
* Command completion in the REPL (pressing tab to get suggestions) has been
fixed for Node 6.9.1+.
* The browser-based tests now include all the tests as the Node-based version.
1.12.1 — DECEMBER 6, 2016
* You can now import a module member named default, e.g. import { default }
from 'lib'. Though like in ES2015, you cannot import an entire module and
name it default (so import default from 'lib' is not allowed).
* Fix regression where from as a variable name was breaking for loop
declarations. For the record, from is not a reserved word in CoffeeScript;
you may use it for variable names. from behaves like a keyword within the
context of import and export statements, and in the declaration of a for
loop; though you should also be able to use variables named from in those
contexts, and the compiler should be able to tell the difference.
1.12.0 — DECEMBER 3, 2016
* CoffeeScript now supports ES2015 tagged template literals. Note that using
tagged template literals in your code makes you responsible for ensuring that
either your runtime supports tagged template literals or that you transpile
the output JavaScript further to a version your target runtime(s) support.
* CoffeeScript now provides a for…from syntax for outputting ES2015 for…of.
(Sorry they couldn’t match, but we came up with for…of first for something
else.) This allows iterating over generators or any other iterable object.
Note that using for…from in your code makes you responsible for ensuring that
either your runtime supports for…of or that you transpile the output
JavaScript further to a version your target runtime(s) support.
* Triple backticks ( ``` ) allow the creation of embedded JavaScript blocks
where escaping single backticks is not required, which should improve
interoperability with ES2015 template literals and with Markdown.
* Within single-backtick embedded JavaScript, backticks can now be escaped via
\` .
* The browser tests now run in the browser again, and are accessible here if
you would like to test your browser.
* CoffeeScript-only keywords in ES2015 imports and exports are now ignored.
* The compiler now throws an error on trying to export an anonymous class.
* Bugfixes related to tokens and location data, for better source maps and
improved compatibility with downstream tools.
1.11.1 — OCTOBER 1, 2016
* Bugfix for shorthand object syntax after interpolated keys.
* Bugfix for indentation-stripping in """ strings.
* Bugfix for not being able to use the name “arguments” for a prototype
property of class.
* Correctly compile large hexadecimal numbers literals to 2e308 (just like all
other large number literals do).
1.11.0 — SEPTEMBER 23, 2016
* CoffeeScript now supports ES2015 import and export syntax.
* Added the -M, --inline-map flag to the compiler, allowing you embed the
source map directly into the output JavaScript, rather than as a separate
file.
* A bunch of fixes for yield:
* yield return can no longer mistakenly be used as an expression.
* yield now mirrors return in that it can be used stand-alone as well as with
expressions. Where you previously wrote yield undefined, you may now write
simply yield. However, this means also inheriting the same syntax
limitations that return has, so these examples no longer compile:
> doubles = ->
> yield for i in [1..3]
> i * 2
> six = ->
> yield
> 2 * 3
* The JavaScript output is a bit nicer, with unnecessary parentheses and
spaces, double indentation and double semicolons around yield no longer
present.
* &&=, ||=, and= and or= no longer accidentally allow a space before the equals
sign.
* Improved several error messages.
* Just like undefined compiles to void 0, NaN now compiles into 0/0 and
Infinity into 2e308.
* Bugfix for renamed destructured parameters with defaults. ({a: b = 1}) -> no
longer crashes the compiler.
* Improved the internal representation of a CoffeeScript program. This is only
noticeable to tools that use CoffeeScript.tokens or CoffeeScript.nodes. Such
tools need to update to take account for changed or added tokens and nodes.
* Several minor bug fixes, including:
* The caught error in catch blocks is no longer declared unnecessarily, and
no longer mistakenly named undefined for catch-less try blocks.
* Unassignable parameter destructuring no longer crashes the compiler.
* Source maps are now used correctly for errors thrown from .coffee.md files.
* coffee -e 'throw null' no longer crashes.
* The REPL no longer crashes when using .exit to exit it.
* Invalid JavaScript is no longer output when lots of for loops are used in
the same scope.
* A unicode issue when using stdin with the CLI.
1.10.0 — SEPTEMBER 2, 2015
* CoffeeScript now supports ES2015-style destructuring defaults.
* (offsetHeight: height) -> no longer compiles. That syntax was accidental and
partly broken. Use ({offsetHeight: height}) -> instead. Object destructuring
always requires braces.
* Several minor bug fixes, including:
* A bug where the REPL would sometimes report valid code as invalid, based on
what you had typed earlier.
* A problem with multiple JS contexts in the jest test framework.
* An error in io.js where strict mode is set on internal modules.
* A variable name clash for the caught error in catch blocks.
1.9.3 — MAY 26, 2015
* Bugfix for interpolation in the first key of an object literal in an implicit
call.
* Fixed broken error messages in the REPL, as well as a few minor bugs with the
REPL.
* Fixed source mappings for tokens at the beginning of lines when compiling
with the --bare option. This has the nice side effect of generating smaller
source maps.
* Slight formatting improvement of compiled block comments.
* Better error messages for on, off, yes and no.
1.9.2 — APRIL 14, 2015
* Fixed a watch mode error introduced in 1.9.1 when compiling multiple files
with the same filename.
* Bugfix for yield around expressions containing this.
* Added a Ruby-style -r option to the REPL, which allows requiring a module
before execution with --eval or --interactive.
* In <script type="text/coffeescript"> tags, to avoid possible duplicate
browser requests for .coffee files, you can now use the data-src attribute
instead of src.
* Minor bug fixes for IE8, strict ES5 regular expressions and Browserify.
1.9.1 — FEBRUARY 17, 2015
* Interpolation now works in object literal keys (again). You can use this to
dynamically name properties.
* Internal compiler variable names no longer start with underscores. This makes
the generated JavaScript a bit prettier, and also fixes an issue with the
completely broken and ungodly way that AngularJS “parses” function arguments.
* Fixed a few yield-related edge cases with yield return and yield throw.
* Minor bug fixes and various improvements to compiler error messages.
1.9.0 — JANUARY 28, 2015
* CoffeeScript now supports ES2015 generators. A generator is simply a function
that yields.
* More robust parsing and improved error messages for strings and regexes —
especially with respect to interpolation.
* Changed strategy for the generation of internal compiler variable names. Note
that this means that @example function parameters are no longer available as
naked example variables within the function body.
* Fixed REPL compatibility with latest versions of Node and Io.js.
* Various minor bug fixes.
1.8.0 — AUGUST 25, 2014
* The --join option of the CLI is now deprecated.
* Source maps now use .js.map as file extension, instead of just .map.
* The CLI now exits with the exit code 1 when it fails to write a file to disk.
* The compiler no longer crashes on unterminated, single-quoted strings.
* Fixed location data for string interpolations, which made source maps out of
sync.
* The error marker in error messages is now correctly positioned if the code is
indented with tabs.
* Fixed a slight formatting error in CoffeeScript’s source map-patched stack
traces.
* The %% operator now coerces its right operand only once.
* It is now possible to require CoffeeScript files from Cakefiles without
having to register the compiler first.
* The CoffeeScript REPL is now exported and can be required using require
'coffeescript/repl'.
* Fixes for the REPL in Node 0.11.
1.7.1 — JANUARY 28, 2014
* Fixed a typo that broke node module lookup when running a script directly
with the coffee binary.
1.7.0 — JANUARY 27, 2014
* When requiring CoffeeScript files in Node you must now explicitly register
the compiler. This can be done with require 'coffeescript/register' or
CoffeeScript.register(). Also for configuration such as Mocha’s, use
coffeescript/register.
* Improved error messages, source maps and stack traces. Source maps now use
the updated //# syntax.
* Leading . now closes all open calls, allowing for simpler chaining syntax.
* Added **, // and %% operators and ... expansion in parameter lists and
destructuring expressions.
* Multiline strings are now joined by a single space and ignore all
indentation. A backslash at the end of a line can denote the amount of
whitespace between lines, in both strings and heredocs. Backslashes correctly
escape whitespace in block regexes.
* Closing brackets can now be indented and therefore no longer cause unexpected
error.
* Several breaking compilation fixes. Non-callable literals (strings, numbers
etc.) don’t compile in a call now and multiple postfix conditionals compile
properly. Postfix conditionals and loops always bind object literals.
Conditional assignment compiles properly in subexpressions. super is
disallowed outside of methods and works correctly inside for loops.
* Formatting of compiled block comments has been improved.
* No more -p folders on Windows.
* The options object passed to CoffeeScript is no longer mutated.
1.6.3 — JUNE 1, 2013
* The CoffeeScript REPL now remembers your history between sessions. Just like
a proper REPL should.
* You can now use require in Node to load .coffee.md Literate CoffeeScript
files. In the browser, text/literate-coffeescript script tags.
* The old coffee --lint command has been removed. It was useful while
originally working on the compiler, but has been surpassed by JSHint. You may
now use -l to pass literate files in over stdio.
* Bugfixes for Windows path separators, catch without naming the error, and
executable-class-bodies-with- prototypal-property-attachment.
1.6.2 — MARCH 17, 2013
* Source maps have been used to provide automatic line-mapping when running
CoffeeScript directly via the coffee command, and for automatic line-mapping
when running CoffeeScript directly in the browser. Also, to provide better
error messages for semantic errors thrown by the compiler — with colors,
even.
* Improved support for mixed literate/vanilla-style CoffeeScript projects, and
generating source maps for both at the same time.
* Fixes for 1.6.x regressions with overriding inherited bound functions, and
for Windows file path management.
* The coffee command can now correctly fork() both .coffee and .js files.
(Requires Node.js 0.9+)
1.6.1 — MARCH 4, 2013
* First release of source maps. Pass the --map flag to the compiler, and off
you go. Direct all your thanks over to Jason Walton.
* Fixed a 1.5.0 regression with multiple implicit calls against an indented
implicit object. Combinations of implicit function calls and implicit objects
should generally be parsed better now — but it still isn’t good style to nest
them too heavily.
* .coffee.md is now also supported as a Literate CoffeeScript file extension,
for existing tooling. .litcoffee remains the canonical one.
* Several minor fixes surrounding member properties, bound methods and super in
class declarations.
1.5.0 — FEBRUARY 24, 2013
* First release of Literate CoffeeScript.
* The CoffeeScript REPL is now based on the Node.js REPL, and should work
better and more familiarly.
* Returning explicit values from constructors is now forbidden. If you want to
return an arbitrary value, use a function, not a constructor.
* You can now loop over an array backwards, without having to manually deal
with the indexes: for item in list by -1
* Source locations are now preserved in the CoffeeScript AST, although source
maps are not yet being emitted.
1.4.0 — OCTOBER 22, 2012
* The CoffeeScript compiler now strips Microsoft’s UTF-8 BOM if it exists,
allowing you to compile BOM-borked source files.
* Fix Node/compiler deprecation warnings by removing registerExtension, and
moving from path.exists to fs.exists.
* Small tweaks to splat compilation, backticks, slicing, and the error for
duplicate keys in object literals.
1.3.3 — MAY 14, 2012
* Due to the new semantics of JavaScript’s strict mode, CoffeeScript no longer
guarantees that constructor functions have names in all runtimes. See #2052
for discussion.
* Inside of a nested function inside of an instance method, it’s now possible
to call super more reliably (walks recursively up).
* Named loop variables no longer have different scoping heuristics than other
local variables. (Reverts #643)
* Fix for splats nested within the LHS of destructuring assignment.
* Corrections to our compile time strict mode forbidding of octal literals.
1.3.1 — APRIL 9, 2012
* CoffeeScript now enforces all of JavaScript’s Strict Mode early syntax errors
at compile time. This includes old-style octal literals, duplicate property
names in object literals, duplicate parameters in a function definition,
deleting naked variables, setting the value of eval or arguments, and more.
See a full discussion at #1547.
* The REPL now has a handy new multi-line mode for entering large blocks of
code. It’s useful when copy-and-pasting examples into the REPL. Enter
multi-line mode with Ctrl-V. You may also now pipe input directly into the
REPL.
* CoffeeScript now prints a Generated by CoffeeScript VERSION header at the top
of each compiled file.
* Conditional assignment of previously undefined variables a or= b is now
considered a syntax error.
* A tweak to the semantics of do, which can now be used to more easily simulate
a namespace: do (x = 1, y = 2) -> …
* Loop indices are now mutable within a loop iteration, and immutable between
them.
* Both endpoints of a slice are now allowed to be omitted for consistency,
effectively creating a shallow copy of the list.
* Additional tweaks and improvements to coffee --watch under Node’s “new” file
watching API. Watch will now beep by default if you introduce a syntax error
into a watched script. We also now ignore hidden directories by default when
watching recursively.
1.2.0 — DECEMBER 17, 2011
* Multiple improvements to coffee --watch and --join. You may now use both
together, as well as add and remove files and directories within a --watch’d
folder.
* The throw statement can now be used as part of an expression.
* Block comments at the top of the file will now appear outside of the safety
closure wrapper.
* Fixed a number of minor 1.1.3 regressions having to do with trailing
operators and unfinished lines, and a more major 1.1.3 regression that caused
bound functions within bound class functions to have the incorrect this.
1.1.3 — NOVEMBER 7, 2011
* Ahh, whitespace. CoffeeScript’s compiled JS now tries to space things out and
keep it readable, as you can see in the examples on this page.
* You can now call super in class level methods in class bodies, and bound
class methods now preserve their correct context.
* JavaScript has always supported octal numbers 010 is 8, and hexadecimal
numbers 0xf is 15, but CoffeeScript now also supports binary numbers: 0b10 is
2.
* The CoffeeScript module has been nested under a subdirectory to make it
easier to require individual components separately, without having to use
npm. For example, after adding the CoffeeScript folder to your path:
require('coffeescript/lexer')
* There’s a new “link” feature in Try CoffeeScript on this webpage. Use it to
get a shareable permalink for your example script.
* The coffee --watch feature now only works on Node.js 0.6.0 and higher, but
now also works properly on Windows.
* Lots of small bug fixes from @michaelficarra, @geraldalewis, @satyr, and
@trevorburnham.
1.1.2 — AUGUST 3, 2011
Fixes for block comment formatting, ?= compilation, implicit calls against
control structures, implicit invocation of a try/catch block, variadic arguments
leaking from local scope, line numbers in syntax errors following heregexes,
property access on parenthesized number literals, bound class methods and super
with reserved names, a REPL overhaul, consecutive compiled semicolons, block
comments in implicitly called objects, and a Chrome bug.
1.1.1 — MAY 9, 2011
Bugfix release for classes with external constructor functions, see issue #1182.
1.1.0 — APRIL 30, 2011
When running via the coffee executable, process.argv and friends now report
coffee instead of node. Better compatibility with Node.js 0.4.x module lookup
changes. The output in the REPL is now colorized, like Node’s is. Giving your
concatenated CoffeeScripts a name when using --join is now mandatory. Fix for
lexing compound division /= as a regex accidentally. All text/coffeescript tags
should now execute in the order they’re included. Fixed an issue with extended
subclasses using external constructor functions. Fixed an edge-case infinite
loop in addImplicitParentheses. Fixed exponential slowdown with long chains of
function calls. Globals no longer leak into the CoffeeScript REPL. Splatted
parameters are declared local to the function.
1.0.1 — JANUARY 30, 2011
Fixed a lexer bug with Unicode identifiers. Updated REPL for compatibility with
Node.js 0.3.7. Fixed requiring relative paths in the REPL. Trailing return and
return undefined are now optimized away. Stopped requiring the core Node.js util
module for back-compatibility with Node.js 0.2.5. Fixed a case where a
conditional return would cause fallthrough in a switch statement. Optimized
empty objects in destructuring assignment.
1.0.0 — DECEMBER 23, 2010
CoffeeScript loops no longer try to preserve block scope when functions are
being generated within the loop body. Instead, you can use the do keyword to
create a convenient closure wrapper. Added a --nodejs flag for passing through
options directly to the node executable. Better behavior around the use of pure
statements within expressions. Fixed inclusive slicing through -1, for all
browsers, and splicing with arbitrary expressions as endpoints.
0.9.6 — DECEMBER 5, 2010
The REPL now properly formats stacktraces, and stays alive through asynchronous
exceptions. Using --watch now prints timestamps as files are compiled. Fixed
some accidentally-leaking variables within plucked closure-loops. Constructors
now maintain their declaration location within a class body. Dynamic object keys
were removed. Nested classes are now supported. Fixes execution context for
naked splatted functions. Bugfix for inversion of chained comparisons. Chained
class instantiation now works properly with splats.
0.9.5 — NOVEMBER 20, 2010
0.9.5 should be considered the first release candidate for CoffeeScript 1.0.
There have been a large number of internal changes since the previous release,
many contributed from satyr’s Coco dialect of CoffeeScript. Heregexes (extended
regexes) were added. Functions can now have default arguments. Class bodies are
now executable code. Improved syntax errors for invalid CoffeeScript. undefined
now works like null, and cannot be assigned a new value. There was a precedence
change with respect to single-line comprehensions: result = i for i in list used
to parse as result = (i for i in list) by default … it now parses as (result =
i) for i in list.
0.9.4 — SEPTEMBER 20, 2010
CoffeeScript now uses appropriately-named temporary variables, and recycles
their references after use. Added require.extensions support for Node.js 0.3.
Loading CoffeeScript in the browser now adds just a single CoffeeScript object
to global scope. Fixes for implicit object and block comment edge cases.
0.9.3 — SEPTEMBER 15, 2010
CoffeeScript switch statements now compile into JS switch statements — they
previously compiled into if/else chains for JavaScript 1.3 compatibility.
Soaking a function invocation is now supported. Users of the RubyMine editor
should now be able to use --watch mode.
0.9.2 — AUGUST 22, 2010
Specifying the start and end of a range literal is now optional, eg. array[3..].
You can now say a not instanceof b. Fixed important bugs with nested significant
and non-significant indentation (Issue #637). Added a --require flag that allows
you to hook into the coffee command. Added a custom jsl.conf file for our
preferred JavaScriptLint setup. Sped up Jison grammar compilation time by
flattening rules for operations. Block comments can now be used with
JavaScript-minifier-friendly syntax. Added JavaScript’s compound assignment
bitwise operators. Bugfixes to implicit object literals with leading number and
string keys, as the subject of implicit calls, and as part of compound
assignment.
0.9.1 — AUGUST 10, 2010
Bugfix release for 0.9.1. Greatly improves the handling of mixed implicit
objects, implicit function calls, and implicit indentation. String and regex
interpolation is now strictly #{ … } (Ruby style). The compiler now takes a
--require flag, which specifies scripts to run before compilation.
0.9.0 — AUGUST 3, 2010
The CoffeeScript 0.9 series is considered to be a release candidate for 1.0;
let’s give her a shakedown cruise. 0.9.0 introduces a massive
backwards-incompatible change: Assignment now uses =, and object literals use :,
as in JavaScript. This allows us to have implicit object literals, and
YAML-style object definitions. Half assignments are removed, in favor of +=,
or=, and friends. Interpolation now uses a hash mark # instead of the dollar
sign $ — because dollar signs may be part of a valid JS identifier. Downwards
range comprehensions are now safe again, and are optimized to straight for loops
when created with integer endpoints. A fast, unguarded form of object
comprehension was added: for all key, value of object. Mentioning the super
keyword with no arguments now forwards all arguments passed to the function, as
in Ruby. If you extend class B from parent class A, if A has an extended method
defined, it will be called, passing in B — this enables static inheritance,
among other things. Cleaner output for functions bound with the fat arrow.
@variables can now be used in parameter lists, with the parameter being
automatically set as a property on the object — useful in constructors and
setter functions. Constructor functions can now take splats.
0.7.2 — JULY 11, 2010
Quick bugfix (right after 0.7.1) for a problem that prevented coffee
command-line options from being parsed in some circumstances.
0.7.1 — JULY 10, 2010
Block-style comments are now passed through and printed as JavaScript block
comments – making them useful for licenses and copyright headers. Better support
for running coffee scripts standalone via hashbangs. Improved syntax errors for
tokens that are not in the grammar.
0.7.0 — JUNE 27, 2010
Official CoffeeScript variable style is now camelCase, as in JavaScript.
Reserved words are now allowed as object keys, and will be quoted for you. Range
comprehensions now generate cleaner code, but you have to specify by -1 if you’d
like to iterate downward. Reporting of syntax errors is greatly improved from
the previous release. Running coffee with no arguments now launches the REPL,
with Readline support. The <- bind operator has been removed from CoffeeScript.
The loop keyword was added, which is equivalent to a while true loop.
Comprehensions that contain closures will now close over their variables, like
the semantics of a forEach. You can now use bound function in class definitions
(bound to the instance). For consistency, a in b is now an array presence check,
and a of b is an object-key check. Comments are no longer passed through to the
generated JavaScript.
0.6.2 — MAY 14, 2010
The coffee command will now preserve directory structure when compiling a
directory full of scripts. Fixed two omissions that were preventing the
CoffeeScript compiler from running live within Internet Explorer. There’s now a
syntax for block comments, similar in spirit to CoffeeScript’s heredocs. ECMA
Harmony DRY-style pattern matching is now supported, where the name of the
property is the same as the name of the value: {name, length}: func. Pattern
matching is now allowed within comprehension variables. unless is now allowed in
block form. until loops were added, as the inverse of while loops. switch
statements are now allowed without switch object clauses. Compatible with
Node.js v0.1.95.
0.6.1 — APRIL 11, 2010
Upgraded CoffeeScript for compatibility with the new Node.js v0.1.90 series.
0.6.0 — APRIL 2, 2010
Trailing commas are now allowed, a-la Python. Static properties may be assigned
directly within class definitions, using @property notation.
0.5.6 — MARCH 22, 2010
Interpolation can now be used within regular expressions and heredocs, as well
as strings. Added the <- bind operator. Allowing assignment to half-expressions
instead of special ||=-style operators. The arguments object is no longer
automatically converted into an array. After requiring coffeescript, Node.js can
now directly load .coffee files, thanks to registerExtension. Multiple splats
can now be used in function calls, arrays, and pattern matching.
0.5.5 — MARCH 7, 2010
String interpolation, contributed by Stan Angeloff. Since --run has been the
default since 0.5.3, updating --stdio and --eval to run by default, pass
--compile as well if you’d like to print the result.
0.5.4 — MARCH 2, 2010
Bugfix that corrects the Node.js global constants __filename and __dirname.
Tweaks for more flexible parsing of nested function literals and
improperly-indented comments. Updates for the latest Node.js API.
0.5.3 — FEBRUARY 26, 2010
CoffeeScript now has a syntax for defining classes. Many of the core components
(Nodes, Lexer, Rewriter, Scope, Optparse) are using them. Cakefiles can use
optparse.coffee to define options for tasks. --run is now the default flag for
the coffee command, use --compile to save JavaScripts. Bugfix for an ambiguity
between RegExp literals and chained divisions.
0.5.2 — FEBRUARY 24, 2010
Added a compressed version of the compiler for inclusion in web pages as
/v2/browser-compiler-legacy/coffeescript.js. It’ll automatically run any script
tags with type text/coffeescript for you. Added a --stdio option to the coffee
command, for piped-in compiles.
0.5.1 — FEBRUARY 23, 2010
Improvements to null soaking with the existential operator, including soaks on
indexed properties. Added conditions to while loops, so you can use them as
filters with when, in the same manner as comprehensions.
0.5.0 — FEBRUARY 20, 2010
CoffeeScript 0.5.0 is a major release, While there are no language changes, the
Ruby compiler has been removed in favor of a self-hosting compiler written in
pure CoffeeScript.
0.3.2 — FEBRUARY 7, 2010
@property is now a shorthand for this.property. Switched the default JavaScript
engine from Narwhal to Node.js. Pass the --narwhal flag if you’d like to
continue using it.
0.3.0 — JANUARY 25, 2010
CoffeeScript 0.3 includes major syntax changes: The function symbol was changed
to ->, and the bound function symbol is now =>. Parameter lists in function
definitions must now be wrapped in parentheses. Added property soaking, with the
?. operator. Made parentheses optional, when invoking functions with arguments.
Removed the obsolete block literal syntax.
0.2.6 — JANUARY 16, 2010
Added Python-style chained comparisons, the conditional existence operator ?=,
and some examples from Beautiful Code. Bugfixes relating to
statement-to-expression conversion, arguments-to-array conversion, and the
TextMate syntax highlighter.
0.2.5 — JANUARY 12, 2010
The conditions in switch statements can now take multiple values at once — If
any of them are true, the case will run. Added the long arrow ==>, which defines
and immediately binds a function to this. While loops can now be used as
expressions, in the same way that comprehensions can. Splats can be used within
pattern matches to soak up the rest of an array.
0.2.4 — JANUARY 11, 2010
Added ECMAScript Harmony style destructuring assignment, for dealing with
extracting values from nested arrays and objects. Added indentation-sensitive
heredocs for nicely formatted strings or chunks of code.
0.2.3 — JANUARY 10, 2010
Axed the unsatisfactory ino keyword, replacing it with of for object
comprehensions. They now look like: for prop, value of object.
0.2.2 — JANUARY 9, 2010
When performing a comprehension over an object, use ino, instead of in, which
helps us generate smaller, more efficient code at compile time. Added :: as a
shorthand for saying .prototype. The “splat” symbol has been changed from a
prefix asterisk *, to a postfix ellipsis ... Added JavaScript’s in operator,
empty return statements, and empty while loops. Constructor functions that start
with capital letters now include a safety check to make sure that the new
instance of the object is returned. The extends keyword now functions
identically to goog.inherits in Google’s Closure Library.
0.2.1 — JANUARY 4, 2010
Arguments objects are now converted into real arrays when referenced.
0.2.0 — JANUARY 4, 2010
Major release. Significant whitespace. Better statement-to-expression
conversion. Splats. Splice literals. Object comprehensions. Blocks. The
existential operator. Many thanks to all the folks who posted issues, with
special thanks to Liam O’Connor-Davis for whitespace and expression help.
0.1.6 — DECEMBER 26, 2009
Bugfix for running coffee --interactive and --run from outside of the
CoffeeScript directory. Bugfix for nested function/if-statements.
0.1.5 — DECEMBER 25, 2009
Array slice literals and array comprehensions can now both take Ruby-style
ranges to specify the start and end. JavaScript variable declaration is now
pushed up to the top of the scope, making all assignment statements into
expressions. You can use \ to escape newlines. The coffeescript command is now
called coffee.
0.1.4 — DECEMBER 24, 2009
The official CoffeeScript extension is now .coffee instead of .cs, which
properly belongs to C#. Due to popular demand, you can now also use = to assign.
Unlike JavaScript, = can also be used within object literals, interchangeably
with :. Made a grammatical fix for chained function calls like func(1)(2)(3)(4).
Inheritance and super no longer use __proto__, so they should be IE-compatible
now.
0.1.3 — DECEMBER 24, 2009
The coffee command now includes --interactive, which launches an interactive
CoffeeScript session, and --run, which directly compiles and executes a script.
Both options depend on a working installation of Narwhal. The aint keyword has
been replaced by isnt, which goes together a little smoother with is. Quoted
strings are now allowed as identifiers within object literals: eg. {"5+5": 10}.
All assignment operators now use a colon: +:, -:, *:, etc.
0.1.2 — DECEMBER 23, 2009
Fixed a bug with calling super() through more than one level of inheritance,
with the re-addition of the extends keyword. Added experimental Narwhal support
(as a Tusk package), contributed by Tom Robinson, including bin/cs as a
CoffeeScript REPL and interpreter. New --no-wrap option to suppress the safety
function wrapper.
0.1.1 — DECEMBER 23, 2009
Added instanceof and typeof as operators.
0.1.0 — DECEMBER 23, 2009
Initial CoffeeScript release.