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Skip to content Vite SearchK Main NavigationGuideConfigPlugins Resources Team Blog Releases Twitter Discord Chat Awesome Vite ViteConf DEV Community Rollup Plugins Compat Changelog Contributing Version Vite 4 Docs Vite 3 Docs Vite 2 Docs English 简体中文 日本語 Español Português 한국어 Deutsch MastodonTwitterDiscordGitHub English 简体中文 日本語 Español Português 한국어 Deutsch Appearance MastodonTwitterDiscordGitHub Menu On this page Sidebar Navigation GUIDE Why Vite Getting Started Features CLI Using Plugins Dependency Pre-Bundling Static Asset Handling Building for Production Deploying a Static Site Env Variables and Modes Server-Side Rendering (SSR) Backend Integration Comparisons Troubleshooting Performance Philosophy Migration from v4 APIS Plugin API HMR API JavaScript API Config Reference On this page Table of Contents for current page * Required Conditional Guard * IntelliSense for TypeScript * hot.accept(cb) * hot.accept(deps, cb) * hot.dispose(cb) * hot.prune(cb) * hot.data * hot.decline() * hot.invalidate(message?: string) * hot.on(event, cb) * hot.off(event, cb) * hot.send(event, data) Beyond Fast ViteConf 2023 Watch the replay! STACKBLITZ NUXTLABS ASTRO STORYBLOK BIT REMIX TAILWIND LABS VUE JOBS DIVRIOTS PREFECT.IO JETBRAINS MUX Dedicated Server für kleine und mittlere Projekte zum kleinen Preis. ads via Carbon On this page HMR API Note This is the client HMR API. For handling HMR update in plugins, see handleHotUpdate. The manual HMR API is primarily intended for framework and tooling authors. As an end user, HMR is likely already handled for you in the framework specific starter templates. Vite exposes its manual HMR API via the special import.meta.hot object: ts interface ImportMeta { readonly hot?: ViteHotContext } type ModuleNamespace = Record<string, any> & { [Symbol.toStringTag]: 'Module' } interface ViteHotContext { readonly data: any accept(): void accept(cb: (mod: ModuleNamespace | undefined) => void): void accept(dep: string, cb: (mod: ModuleNamespace | undefined) => void): void accept( deps: readonly string[], cb: (mods: Array<ModuleNamespace | undefined>) => void, ): void dispose(cb: (data: any) => void): void prune(cb: (data: any) => void): void invalidate(message?: string): void // `InferCustomEventPayload` provides types for built-in Vite events on<T extends string>( event: T, cb: (payload: InferCustomEventPayload<T>) => void, ): void off<T extends string>( event: T, cb: (payload: InferCustomEventPayload<T>) => void, ): void send<T extends string>(event: T, data?: InferCustomEventPayload<T>): void } REQUIRED CONDITIONAL GUARD First of all, make sure to guard all HMR API usage with a conditional block so that the code can be tree-shaken in production: js if (import.meta.hot) { // HMR code } INTELLISENSE FOR TYPESCRIPT Vite provides type definitions for import.meta.hot in vite/client.d.ts. You can create an env.d.ts in the src directory so TypeScript picks up the type definitions: ts /// <reference types="vite/client" /> HOT.ACCEPT(CB) For a module to self-accept, use import.meta.hot.accept with a callback which receives the updated module: js export const count = 1 if (import.meta.hot) { import.meta.hot.accept((newModule) => { if (newModule) { // newModule is undefined when SyntaxError happened console.log('updated: count is now ', newModule.count) } }) } A module that "accepts" hot updates is considered an HMR boundary. Vite's HMR does not actually swap the originally imported module: if an HMR boundary module re-exports imports from a dep, then it is responsible for updating those re-exports (and these exports must be using let). In addition, importers up the chain from the boundary module will not be notified of the change. This simplified HMR implementation is sufficient for most dev use cases, while allowing us to skip the expensive work of generating proxy modules. Vite requires that the call to this function appears as import.meta.hot.accept( (whitespace-sensitive) in the source code in order for the module to accept update. This is a requirement of the static analysis that Vite does to enable HMR support for a module. HOT.ACCEPT(DEPS, CB) A module can also accept updates from direct dependencies without reloading itself: js import { foo } from './foo.js' foo() if (import.meta.hot) { import.meta.hot.accept('./foo.js', (newFoo) => { // the callback receives the updated './foo.js' module newFoo?.foo() }) // Can also accept an array of dep modules: import.meta.hot.accept( ['./foo.js', './bar.js'], ([newFooModule, newBarModule]) => { // The callback receives an array where only the updated module is // non null. If the update was not successful (syntax error for ex.), // the array is empty }, ) } HOT.DISPOSE(CB) A self-accepting module or a module that expects to be accepted by others can use hot.dispose to clean-up any persistent side effects created by its updated copy: js function setupSideEffect() {} setupSideEffect() if (import.meta.hot) { import.meta.hot.dispose((data) => { // cleanup side effect }) } HOT.PRUNE(CB) Register a callback that will call when the module is no longer imported on the page. Compared to hot.dispose, this can be used if the source code cleans up side-effects by itself on updates and you only need to clean-up when it's removed from the page. Vite currently uses this for .css imports. js function setupOrReuseSideEffect() {} setupOrReuseSideEffect() if (import.meta.hot) { import.meta.hot.prune((data) => { // cleanup side effect }) } HOT.DATA The import.meta.hot.data object is persisted across different instances of the same updated module. It can be used to pass on information from a previous version of the module to the next one. Note that re-assignment of data itself is not supported. Instead, you should mutate properties of the data object so information added from other handlers are preserved. js // ok import.meta.hot.data.someValue = 'hello' // not supported import.meta.hot.data = { someValue: 'hello' } HOT.DECLINE() This is currently a noop and is there for backward compatibility. This could change in the future if there is a new usage for it. To indicate that the module is not hot-updatable, use hot.invalidate(). HOT.INVALIDATE(MESSAGE?: STRING) A self-accepting module may realize during runtime that it can't handle a HMR update, and so the update needs to be forcefully propagated to importers. By calling import.meta.hot.invalidate(), the HMR server will invalidate the importers of the caller, as if the caller wasn't self-accepting. This will log a message both in the browser console and in the terminal. You can pass a message to give some context on why the invalidation happened. Note that you should always call import.meta.hot.accept even if you plan to call invalidate immediately afterwards, or else the HMR client won't listen for future changes to the self-accepting module. To communicate your intent clearly, we recommend calling invalidate within the accept callback like so: js import.meta.hot.accept((module) => { // You may use the new module instance to decide whether to invalidate. if (cannotHandleUpdate(module)) { import.meta.hot.invalidate() } }) HOT.ON(EVENT, CB) Listen to an HMR event. The following HMR events are dispatched by Vite automatically: * 'vite:beforeUpdate' when an update is about to be applied (e.g. a module will be replaced) * 'vite:afterUpdate' when an update has just been applied (e.g. a module has been replaced) * 'vite:beforeFullReload' when a full reload is about to occur * 'vite:beforePrune' when modules that are no longer needed are about to be pruned * 'vite:invalidate' when a module is invalidated with import.meta.hot.invalidate() * 'vite:error' when an error occurs (e.g. syntax error) * 'vite:ws:disconnect' when the WebSocket connection is lost * 'vite:ws:connect' when the WebSocket connection is (re-)established Custom HMR events can also be sent from plugins. See handleHotUpdate for more details. HOT.OFF(EVENT, CB) Remove callback from the event listeners HOT.SEND(EVENT, DATA) Send custom events back to Vite's dev server. If called before connected, the data will be buffered and sent once the connection is established. See Client-server Communication for more details. Suggest changes to this page Previous pagePlugin API Next pageJavaScript API Released under the MIT License. (a1c9221a) Copyright © 2019-present Evan You & Vite Contributors