webpack-howto#

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教程目标#

This is a cookbook of how to get things done with webpack. This includes most things we use at Instagram and nothing we don't use.My advice: start with this as your webpack docs, then look at the official docs for clarification.

这是Instagram公司的使用的webpack配置，可以从这个文档看起，然后以官方网站为准。

准备#

• You know browserify, RequireJS or something similar
• You see the value in:
  • Bundle splitting
  • Async loading
  • Packaging static assets like images and CSS

1. 为什么选择 webpack?#

• It's like browserify but can split your app into multiple files. If you have multiple pages in a single-page app, the user only downloads code for just that page. If they go to another page, they don't redownload common code. 类似于 browserify，同时可以分割你的APP成为多个文件，如果一个SPA中有多个页面，用户可以下载当前页面需要的JS；如果跳转到另一个界面，不需要下载相同的代码。
• It often replaces grunt or gulp because it can build and bundle CSS, preprocessed CSS, compile-to-JS languages and images, among other things. 可以实现 grunt gulp 类似的功能。

It supports AMD and CommonJS, among other module systems (Angular, ES6). If you don't know what to use, use CommonJS.

2. Webpack for Browserify people#

These are equivalent:

browserify main.js > bundle.js
webpack main.js bundle.js

However, webpack is more powerful than Browserify, so you generally want to make a webpack.config.js to keep things organized:

// webpack.config.js
module.exports = {
  entry: './main.js',
  output: {
    filename: 'bundle.js'       
  }
};

This is just JS, so feel free to put Real Code in there.

相对于 browserify , webpack 可以设置配置文件

3. How to invoke webpack#

怎样使用 webpack? 在目录中增加配置文件，打包时可以增加参数配置不同的打包环境

Switch to the directory containing webpack.config.js and run:

• webpack for building once for development
• webpack -p for building once for production (minification)
• webpack --watch for continuous incremental build in development (fast!)
• webpack -d to include source maps

4. Compile-to-JS languages#

怎样编译成JS文件（typescript coffeescript ES6 编译成 Js）各种 loader 预处理

webpack's equivalent of browserify transforms and RequireJS plugins is a loader. Here's how you can teach webpack to load CoffeeScript and Facebook JSX+ES6 support (you must npm install babel-loader coffee-loader):

See also the babel-loader installation instructions for additional dependencies (tl;dr run npm install babel-core babel-preset-es2015 babel-preset-react).

// webpack.config.js
module.exports = {
  entry: './main.js',
  output: {
    filename: 'bundle.js'       
  },
  module: {
    loaders: [
      { test: /\.coffee$/, loader: 'coffee-loader' },
      {
        test: /\.js$/,
        loader: 'babel-loader',
        query: {
          presets: ['es2015', 'react']
        }
      }
    ]
  }
};

To enable requiring files without specifying the extension, you must add a resolve.extensions parameter specifying which files webpack searches for:

// webpack.config.js
module.exports = {
  entry: './main.js',
  output: {
    filename: 'bundle.js'       
  },
  module: {
    loaders: [
      { test: /\.coffee$/, loader: 'coffee-loader' },
      {
        test: /\.js$/,
        loader: 'babel-loader',
        query: {
          presets: ['es2015', 'react']
        }
      }
    ]
  },
  resolve: {
    // you can now require('file') instead of require('file.coffee')
    extensions: ['', '.js', '.json', '.coffee'] 
  }
};

5. Stylesheets and images#

First update your code to require() your static assets (named as they would with node's require()):

require('./bootstrap.css');
require('./myapp.less');

var img = document.createElement('img');
img.src = require('./glyph.png');

When you require CSS (or less, etc), webpack inlines the CSS as a string inside the JS bundle and require() will insert a <style> tag into the page. When you require images, webpack inlines a URL to the image into the bundle and returns it from require().

But you need to teach webpack to do this (again, with loaders):

// webpack.config.js
module.exports = {
  entry: './main.js',
  output: {
    path: './build', // This is where images AND js will go
    publicPath: 'http://mycdn.com/', // This is used to generate URLs to e.g. images
    filename: 'bundle.js'
  },
  module: {
    loaders: [
      { test: /\.less$/, loader: 'style-loader!css-loader!less-loader' }, // use ! to chain loaders
      { test: /\.css$/, loader: 'style-loader!css-loader' },
      { test: /\.(png|jpg)$/, loader: 'url-loader?limit=8192' } // inline base64 URLs for <=8k images, direct URLs for the rest
    ]
  }
};

6. Feature flags#

We have code we want to gate only to our dev environments (like logging) and our internal dogfooding servers (like unreleased features we're testing with employees). In your code, refer to magic globals:

Then teach webpack those magic globals:

Then you can build with BUILD_DEV=1 BUILD_PRERELEASE=1 webpack from the console. Note that since webpack -p runs uglify dead-code elimination, anything wrapped in one of these blocks will be stripped out, so you won't leak secret features or strings.

7. Multiple entrypoints#

Let's say you have a profile page and a feed page. You don't want to make the user download the code for the feed if they just want the profile. So make multiple bundles: create one "main module" (called an entrypoint) per page:

For profile, insert <script src="build/Profile.js"></script> into your page. Do a similar thing for feed.

8. Optimizing common code#

Feed and Profile share a lot in common (like React and the common stylesheets and components). webpack can figure out what they have in common and make a shared bundle that can be cached between pages:

Add <script src="build/common.js"></script> before the script tag you added in the previous step and enjoy the free caching.

9. Async loading#

CommonJS is synchronous but webpack provides a way to asynchronously specify dependencies. This is useful for client-side routers, where you want the router on every page, but you don't want to have to download features until you actually need them.

Specify the split point where you want to load asynchronously. For example:

webpack will do the rest and generate extra chunk files and load them for you.

webpack will assume that those files are in your root directory when you load then into a html script tag for example. You can use output.publicPath to configure that.

Additional resources#

Take a look at a real world example on how a successful team is leveraging webpack: http://youtu.be/VkTCL6Nqm6Y This is Pete Hunt at OSCon talking about webpack at Instagram.com

FAQ#

webpack doesn't seem modular#

webpack is extremely modular. What makes webpack great is that it lets plugins inject themselves into more places in the build process when compared to alternatives like browserify and requirejs. Many things that may seem built into the core are just plugins that are loaded by default and can be overridden (i.e. the CommonJS require() parser).