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vite

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Vite is an opinionated web dev build tool that serves your code via native ES Module imports during dev and bundles it with Rollup for production.

  • Lightning fast cold server start
  • Instant hot module replacement (HMR)
  • True on-demand compilation
  • More details in How and Why

Status

In beta and will likely release 1.0 soon.

Getting Started

Note to Vue users: Vite currently only works with Vue 3.x. This also means you can't use libraries that are not yet compatible with Vue 3.

$ npm init vite-app <project-name>
$ cd <project-name>
$ npm install
$ npm run dev

If using Yarn:

$ yarn create vite-app <project-name>
$ cd <project-name>
$ yarn
$ yarn dev

Although Vite is primarily designed to work with Vue 3, it can support other frameworks as well. For example, try npm init vite-app --template react or --template preact.

Using master branch

If you can't wait for a new release to test latest features, clone the vite to your local machine and execute following commands:

yarn
yarn build
yarn link

Then go to your vite based project and run yarn link vite. Now restart the development server (yarn dev) to ride on the bleeding edge!

Browser Support

Vite requires native ES module imports during development. The production build also relies on dynamic imports for code-splitting (which can be polyfilled).

Vite assumes you are targeting modern browsers and therefore does not perform any compatibility-oriented code transforms by default. Technically, you can add autoprefixer yourself using a PostCSS config file, or add necessary polyfills and post-processing steps to make your code work in legacy browsers - however that is not Vite's concern by design.

Features

Vite tries to mirror the default configuration in vue-cli as much as possible. If you've used vue-cli or other webpack-based boilerplates before, you should feel right at home. That said, do expect things to be different here and there.

Bare Module Resolving

Native ES imports doesn't support bare module imports like

import { createApp } from 'vue'

The above will throw an error by default. Vite detects such bare module imports in all served .js files and rewrites them with special paths like /@modules/vue. Under these special paths, Vite performs module resolution to locate the correct files from your installed dependencies.

Note that vue has special treatment - if it isn't installed in the project locally, Vite will fallback to the version from its own dependencies. If you have Vite installed globally, this makes it possible to quickly prototype with Vue without installing anything locally.

Hot Module Replacement

  • The vue, react and preact templates of create-vite-app all come with HMR out of the box.

  • For manual HMR, an API is provided via import.meta.hot.

    For a module to self-accept, use import.meta.hot.accept:

    export const count = 1
    
    // the conditional check is required so that HMR related code can be
    // dropped in production
    if (import.meta.hot) {
      import.meta.hot.accept((newModule) => {
        console.log('updated: count is now ', newModule.count)
      })
    }

    A module can also accept updates from direct dependencies without reloading itself, using import.meta.hot.acceptDeps:

    import { foo } from './foo.js'
    
    foo()
    
    if (import.meta.hot) {
      import.meta.hot.acceptDeps('./foo.js', (newFoo) => {
        // the callback receives the updated './foo.js' module
        newFoo.foo()
      })
    
      // Can also accept an array of dep modules:
      import.meta.hot.acceptDeps(['./foo.js', './bar.js'], ([newFooModule, newBarModule]) => {
        // the callback receives the updated modules in an Array
      })
    }

    A self-accepting module, or a module that expects to be accepted by others can use hot.dispose to cleanup any persistent side effects created by its updated copy:

    function setupSideEffect() {}
    
    setupSideEffect()
    
    if (import.meta.hot) {
      import.meta.hot.dispose((data) => {
        // cleanup side effect
      })
    }

    For the full API, consult hmr.d.ts.

    Note that Vite's HMR does not actually swap the originally imported module: if an accepting 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 accepting 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.

TypeScript

Vite supports importing .ts files and <script lang="ts"> in Vue SFCs out of the box.

Vite only performs transpilation on .ts files and does NOT perform type checking. It assumes type checking is taken care of by your IDE and build process (you can run tsc --noEmit in the build script).

Vite uses esbuild to transpile TypeScript into JavaScript which is about 20~30x faster than vanilla tsc, and HMR updates can reflect in the browser in under 50ms.

Note that because esbuild only performs transpilation without type information, it doesn't support certain features like const enum and implicit type-only imports. You must set "isolatedModules": true in your tsconfig.json under compilerOptions so that TS will warn you against the features that do not work with isolated transpilation.

CSS / JSON Importing

You can directly import .css and .json files from JavaScript (including <script> tags of *.vue files, of course).

  • .json files export their content as an object that is the default export.

  • .css files do not export anything unless it ends with .module.css (See CSS Modules below). Importing them leads to the side effect of them being injected to the page during dev, and being included in the final style.css of the production build.

Both CSS and JSON imports also support Hot Module Replacement.

Asset URL Handling

You can reference static assets in your *.vue templates, styles and plain .css files either using absolute public paths (based on project root) or relative paths (based on your file system). The latter is similar to the behavior you are used to if you have used vue-cli or webpack's file-loader.

All referenced assets, including those using absolute paths, will be copied to the dist folder with a hashed file name in the production build. Never-referenced assets will not be copied. Similar to vue-cli, image assets smaller than 4kb will be base64 inlined.

All static path references, including absolute paths, should be based on your working directory structure.

The public Directory

The public directory under project root can be used as an escape hatch to provide static assets that either are never referenced in source code (e.g. robots.txt), or must retain the exact same file name (without hashing).

Assets placed in public will be copied to the root of the dist directory as-is.

Note that you should reference files placed in public using root absolute path - for example, public/icon.png should always be referenced in source code as /icon.png.

Public Base Path

If you are deploying your project under a nested public path, simply specify --base=/your/public/path/ and all asset paths will be rewritten accordingly.

For dynamic path references, there are two options:

  • You can get the resolved public path of a static asset file by importing it from JavaScript. e.g. import path from './foo.png' will give you its resolved public path as a string.

  • If you need to concatenate paths on the fly, you can use the globally injected import.meta.env.BASE_URL variable with will be the public base path. Note this variable is statically replaced during build so it must appear exactly as-is (i.e. import.meta.env['BASE_URL'] won't work).

PostCSS

Vite automatically applies your PostCSS config to all styles in *.vue files and imported plain .css files. Just install necessary plugins and add a postcss.config.js in your project root.

CSS Modules

Note that you do not need to configure PostCSS if you want to use CSS Modules: it works out of the box. Inside *.vue components you can use <style module>, and for plain .css files, you need to name CSS modules files as *.module.css which allows you to import the naming hash from it.

CSS Pre-Processors

Because Vite targets modern browsers only, it is recommended to use native CSS variables with PostCSS plugins that implement CSSWG drafts (e.g. postcss-nesting) and author plain, future-standards-compliant CSS. That said, if you insist on using a CSS pre-processor, you can install the corresponding pre-processor and just use it:

yarn add -D sass
<style lang="scss">
/* use scss */
</style>

Or import them from JavaScript:

import './style.scss'

JSX

.jsx and .tsx files are also supported. JSX transpilation is also handled via esbuild.

The default JSX configuration works out of the box with Vue 3 (note there is currently no JSX-based HMR for Vue):

import { createApp } from 'vue'

function App() {
  return <Child>{() => 'bar'}</Child>
}

function Child(_, { slots }) {
  return <div onClick={() => console.log('hello')}>{slots.default()}</div>
}

createApp(App).mount('#app')

Currently this is auto-importing a jsx compatible function that converts esbuild-produced JSX calls into Vue 3 compatible vnode calls, which is sub-optimal. Vue 3 will eventually provide a custom JSX transform that can take advantage of Vue 3's runtime fast paths.

JSX with React/Preact

There are two other presets provided: react and preact. You can specify the preset by running Vite with --jsx react or --jsx preact.

If you need a custom JSX pragma, JSX can also be customized via --jsx-factory and --jsx-fragment flags from the CLI or jsx: { factory, fragment } from the API. For example, you can run vite --jsx-factory=h to use h for JSX element creation calls. In the config (see Config File below), it can be specified as:

// vite.config.js
module.exports = {
  jsx: {
    factory: 'h',
    fragment: 'Fragment'
  }
}

Note that for the Preact preset, h is also auto injected so you don't need to manually import it. However, this may cause issues if you are using .tsx with Preact since TS expects h to be explicitly imported for type inference. In that case, you can use the explicit factory config shown above which disables the auto h injection.

Web Assembly

1.0.0-beta.3+

Pre-compiled .wasm files can be directly imported - the default export will be a initialization function that returns a Promise of the exports object of the wasm instance:

import init from './example.wasm'

init().then(exports => {
  exports.test()
})

The init function can also take the imports object which is passed along to WebAssembly.instantiate as its second argument:

init({
  imports: {
    someFunc: () => { /* ... */ }
  }
}).then(() => { /* ... */ })

In the production build, .wasm files smaller than assetInlineLimit will be inlined as base64 strings. Otherwise they will be copied to the dist directory as an asset and fetched on demand.

Inline Web Workers

1.0.0-beta.3+

A web worker script can be directly imported by appending ?worker to the import request. The default export will be a custom worker constructor:

import MyWorker from './worker?worker'

const worker = new MyWorker()

In the production build, workers imported this way are inlined into the bundle as base64 strings.

The worker script can also use import statements instead of importScripts() - note during dev this relies on browser native support and currently only works in Chrome, but for the production build it is compiled away.

If you do not wish to inline the worker, you should place your worker scripts in public and initialize the worker via new Worker('/worker.js').

Config File

You can create a vite.config.js or vite.config.ts file in your project. Vite will automatically use it if one is found in the current working directory. You can also explicitly specify a config file via vite --config my-config.js.

In addition to options mapped from CLI flags, it also supports alias, transforms, and plugins (which is a subset of the config interface). For now, see config.ts for full details before more thorough documentation is available.

Custom Blocks

Custom blocks in Vue SFCs are also supported. To use custom blocks, specify transform functions for custom blocks using the vueCustomBlockTransforms option in the config file:

// vite.config.js
module.exports = {
  vueCustomBlockTransforms: {
    i18n: ({ code }) => {
      // return transformed code
    }
  }
}

HTTPS/2

Starting the server with --https will automatically generate a self-signed cert and start the server with TLS and HTTP/2 enabled.

Custom certs can also be provided by using the httpsOptions option in the config file, which accepts key, cert, ca and pfx as in Node https.ServerOptions.

Dev Server Proxy

You can use the proxy option in the config file to configure custom proxies for the dev server. Vite uses koa-proxies which in turn uses http-proxy. Each key can be a path Full options here.

Example:

// vite.config.js
module.exports = {
  proxy: {
    // string shorthand
    '/foo': 'http://localhost:4567/foo',
    // with options
    '/api': {
      target: 'http://jsonplaceholder.typicode.com',
      changeOrigin: true,
      rewrite: path => path.replace(/^\/api/, '')
    }
  }
}

Production Build

Vite does utilize bundling for production builds, because native ES module imports result in waterfall network requests that are simply too punishing for page load time in production.

You can run vite build to bundle the app.

Internally, we use a highly opinionated Rollup config to generate the build. The build is configurable by passing on most options to Rollup - and most non-rollup string/boolean options have mapping flags in the CLI (see build/index.ts for full details).

Modes and Environment Variables

The mode option is used to specify the value of import.meta.env.MODE and the corresponding environment variables files that needs to be loaded.

By default, there are two modes:

  • development is used by vite and vite serve
  • production is used by vite build

You can overwrite the default mode used for a command by passing the --mode option flag. For example, if you want to use development variables in the build command:

vite build --mode development

When running vite, environment variables are loaded from the following files in your project root:

.env                # loaded in all cases
.env.local          # loaded in all cases, ignored by git
.env.[mode]         # only loaded in specified env mode
.env.[mode].local   # only loaded in specified env mode, ignored by git

Note: only variables prefixed with VITE_ are exposed to your code. e.g. VITE_SOME_KEY=123 will be exposed as import.meta.env.VITE_SOME_KEY, but SOME_KEY=123 will not. This is because the .env files may be used by some users for server-side or build scripts and may contain sensitive information that should not be exposed in code shipped to browsers.

API

Dev Server

You can customize the server using the API. The server can accept plugins which have access to the internal Koa app instance:

const { createServer } = require('vite')

const myPlugin = ({
  root, // project root directory, absolute path
  app, // Koa app instance
  server, // raw http server instance
  watcher // chokidar file watcher instance
}) => {
  app.use(async (ctx, next) => {
    // You can do pre-processing here - this will be the raw incoming requests
    // before vite touches it.
    if (ctx.path.endsWith('.scss')) {
      // Note vue <style lang="xxx"> are supported by
      // default as long as the corresponding pre-processor is installed, so this
      // only applies to <link ref="stylesheet" href="*.scss"> or js imports like
      // `import '*.scss'`.
      console.log('pre processing: ', ctx.url)
      ctx.type = 'css'
      ctx.body = 'body { border: 1px solid red }'
    }

    // ...wait for vite to do built-in transforms
    await next()

    // Post processing before the content is served. Note this includes parts
    // compiled from `*.vue` files, where <template> and <script> are served as
    // `application/javascript` and <style> are served as `text/css`.
    if (ctx.response.is('js')) {
      console.log('post processing: ', ctx.url)
      console.log(ctx.body) // can be string or Readable stream
    }
  })
}

createServer({
  configureServer: [myPlugin]
}).listen(3000)

Build

Check out the full options interface in build/index.ts.

const { build } = require('vite')

;(async () => {
  // All options are optional.
  // check out `src/node/build/index.ts` for full options interface.
  const result = await build({
    rollupInputOptions: {
      // https://rollupjs.org/guide/en/#big-list-of-options
    },
    rollupOutputOptions: {
      // https://rollupjs.org/guide/en/#big-list-of-options
    },
    rollupPluginVueOptions: {
      // https://github.com/vuejs/rollup-plugin-vue/tree/next#options
    }
    // ...
  })
})()

How and Why

How is This Different from vue-cli or Other Bundler-based Solutions?

The primary difference is that for Vite there is no bundling during development. The ES Import syntax in your source code is served directly to the browser, and the browser parses them via native <script module> support, making HTTP requests for each import. The dev server intercepts the requests and performs code transforms if necessary. For example, an import to a *.vue file is compiled on the fly right before it's sent back to the browser.

There are a few advantages of this approach:

  • Since there is no bundling work to be done, the server cold start is extremely fast.

  • Code is compiled on demand, so only code actually imported on the current screen is compiled. You don't have to wait until your entire app to be bundled to start developing. This can be a huge difference in apps with dozens of screens.

  • Hot module replacement (HMR) performance is decoupled from the total number of modules. This makes HMR consistently fast no matter how big your app is.

Full page reload could be slightly slower than a bundler-based setup, since native ES imports result in network waterfalls with deep import chains. However since this is local development, the difference should be trivial compared to actual compilation time. (There is no compile cost on page reload since already compiled files are cached in memory.)

Finally, because compilation is still done in Node, it can technically support any code transforms a bundler can, and nothing prevents you from eventually bundling the code for production. In fact, Vite provides a vite build command to do exactly that so the app doesn't suffer from network waterfall in production.

How is This Different from es-dev-server?

es-dev-server is a great project and we did take some inspiration from it when refactoring Vite in the early stages. That said, here is why Vite is different from es-dev-server and why we didn't just implement Vite as a middleware for es-dev-server:

  • One of Vite's primary goal was to support Hot Module Replacement, but es-dev-server internals is a bit too opaque to get this working nicely via a middleware.

  • Vite aims to be a single tool that integrates both the dev and the build process. You can use Vite to both serve and bundle the same source code, with zero configuration.

  • Vite is more opinionated on how certain types of imports are handled, e.g. .css and static assets. The handling is similar to vue-cli for obvious reasons.

How is This Different from Snowpack?

Both Snowpack v2 and Vite offer native ES module import based dev servers. Vite's dependency pre-optimization is also heavily inspired by Snowpack v1. Both projects share similar performance characteristics when it comes to development feedback speed. Some notable differences are:

  • Vite was created to tackle native ESM-based HMR. When Vite was first released with working ESM-based HMR, there was no other project actively trying to bring native ESM based HMR to production.

    Snowpack v2 initially did not offer HMR support but added it in a later release, making the scope of two projects much closer. Vite and Snowpack has collaborated on a common API spec for ESM HMR, but due to the constraints of different implementation strategies, the two projects still ship slightly different APIs.

  • Both solutions can also bundle the app for production, but Vite uses Rollup with built-in config while Snowpack delegates it to Parcel/webpack via additional plugins. Vite will in most cases build faster and produce smaller bundles. In addition, a tighter integration with the bundler makes it easier to author Vite transforms and plugins that modify dev/build configs at the same.

  • Vue support is a first-class feature in Vite. For example, Vite provides a much more fine-grained HMR integration with Vue, and the build config is fined tuned to produce the most efficient bundle.

Contribution

See Contributing Guide.

Trivia

vite is the french word for "fast" and is pronounced /vit/.

License

MIT

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Native-ESM powered web dev build tool. It's fast.

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