vite ⚡

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

Still experimental, but we intend to make it suitable for production.

Getting Started

$ npx create-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 actually support other frameworks as well. For example, try npx create-vite-app with --template react or --template preact.

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.

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 on disk:

vue has special handling: you don't need to install it since Vite will serve it by default. But if you want to use a specific version of vue (only supports Vue 3.x), you can install vue locally into node_modules and it will be preferred (@vue/compiler-sfc of the same version will also need to be installed).
If a web_modules directory (generated by Snowpack) is present, we will try to locate it.
Finally we will try resolving the module from node_modules, using the package's module entry if available.

Hot Module Replacement

*.vue files come with HMR out of the box.

For *.js files, a simple HMR API is provided:

import { foo } from './foo.js'
import { hot } from 'vite/hmr'

foo()

// this code will be stripped out when building
if (__DEV__) {
  hot.accept('./foo.js', (newFoo) => {
    // the callback receives the updated './foo.js' module
    newFoo.foo()
  })

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

Modules can also be self-accepting:

import { hot } from 'vite/hmr'

export const count = 1

// this code will be stripped out when building
if (__DEV__) {
  hot.accept((newModule) => {
    console.log('updated: count is now ', newModule.count)
  })
}

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:

import { hot } from 'vite/hmr'

function setupSideEffect() {}
function cleanupSideEffect() {}

setupSideEffect()

if (__DEV__) {
  hot.dispose(cleanupSideEffect)
}

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.

The exception is the public directory - assets placed in this directory will be copied to the dist directory as-is. It can be used to provide assets that are never referenced in your code - e.g. robots.txt.

All static path references, including absolute paths and those starting with /public, should be based on your working directory structure. 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 __BASE__ variable with will be the public base path.

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>

Note importing CSS / preprocessor files from .js files, and HMR from imported pre-processor files are currently not supported, but can be in the future.

JSX

.jsx and .tsx files are also supported. JSX transpilation is also handled via esbuild. Note that there is currently no auto-HMR support for any JSX-based usage.

The default JSX configuration works out of the box with Vue 3:

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. For the Preact preset, h is also auto injected so you don't need to manually import it.

Because React doesn't ship ES module builds, you either need to use es-react, or pre-bundle React into a ES module with Snowpack. Easiest way to get it running is:

import { React, ReactDOM } from 'https://unpkg.com/es-react'

ReactDOM.render(<h1>Hello, what!</h1>, document.getElementById('app'))

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.

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).

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.

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({
  plugins: [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.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?

Snowpack 2 is closer to Vite in scope - both offer bundle-free dev servers and can bundle the app for production. Some notable differences are:

Specifically for Vue, Vite provides built-in HMR, while Snowpack simply reloads the page on any file edit. Since both solutions rely on native ES imports, the network waterfall of full page reloads can actually become the bottleneck in edit-to-feedback speed. HMR allows you to avoid reloading the page for a decent part of your development time.
Vite is a bit more opinionated and aims to minimize the amount of configuration required. All the features listed above like TypeScript transpilation, CSS import, and PostCSS support just work out of the box.
While Vite can technically be used to develop apps with any framework, its main focus is to provide the best Vue development experience possible. 3rd party framework support is currently not a priority in the roadmap. On the other hand, Snowpack aims to be more flexible and support multiple frameworks at the same time.

That said, because Vite supports resolving web_modules, you can use Snowpack to pre-bundle dependencies (which reduces network requests during dev) in your Vite project to speed up full page reloads.

TODOs

Config file support
- Define config options
- Define plugin format

Trivia

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

License

MIT

FredKSchott/vite