HappyPack

HappyPack makes initial webpack builds faster by transforming files in parallel.

Usage

npm install --save-dev happypack

HappyPack provides both a plugin and a loader in order to do its job so you must use both to enable it.

Normally, you define loader rules to tell webpack how to process certain files. With HappyPack, you switch things around so that you pass the loaders to HappyPack's plugin and instead tell webpack to use happypack/loader.

Below is a sample configuration that shows those steps in action.

// @file: webpack.config.js
const HappyPack = require('happypack');

exports.module = {
  rules: [
    {
      test: /.js$/,
      // 1) replace your original list of loaders with "happypack/loader":
      // loaders: [ 'babel-loader?presets[]=es2015' ],
      use: 'happypack/loader',
      include: [ /* ... */ ],
      exclude: [ /* ... */ ]
    }
  ]
};

exports.plugins = [
  // 2) create the plugin:
  new HappyPack({
    // 3) re-add the loaders you replaced above in #1:
    loaders: [ 'babel-loader?presets[]=es2015' ]
  })
];

That's it. Now sources that match .js$ will be handed off to HappyPack which will transform them in parallel using the loaders you specified (babel-loader in this example.)

Configuration

These are the parameters you can pass to the plugin when you instantiate it. loaders is the only required parameter.

`loaders: Array`

Each entry consists of the name (or absolute path) of the loader that would transform the files and an optional query string to pass to it. This looks similar to what you'd pass to webpack's loader config.

Heads up!

HappyPack doesn't work with all webpack loaders as some loader API are not supported.

See this wiki page for more details on current Loader API support.

The following notations are officially supported and are all equivalent:

{
  loaders: [
    // a string with embedded query for options
    'babel-loader?presets[]=es2015',

    {
      loader: 'babel-loader'
    },

    // "query" string
    {
      loader: 'babel-loader',
      query:  '?presets[]=es2015'
    },

    // "query" object
    {
      loader: 'babel-loader',
      query: {
        presets: [ 'es2015' ]
      }
    },

    // Webpack 2+ "options" object instead of "query"
    {
      loader: 'babel-loader',
      options: {
        presets: [ 'es2015' ]
      }
    }
  ]
}

`id: String`

A unique id for this happy plugin. This is used by the loader to know which plugin it's supposed to talk to.

Normally, you would not need to specify this unless you have more than one HappyPack plugin defined, in which case you'll need distinct IDs to tell them apart. See this section for more information.

Defaults to: "1"

`threads: Number`

This number indicates how many Node VMs HappyPack will spawn for compiling the source files. After a lot of tinkering, I found 4 to yield the best results. There's certainly a diminishing return on this value and increasing beyond 8 actually slowed things down for me.

Keep in mind that this is only relevant when performing the initial build as HappyPack will switch into a synchronous mode afterwards (i.e. in watch mode.)

Defaults to: 3

`threadPool: HappyThreadPool`

A pre-defined thread-pool to use for retrieving worker threads. Normally, this is managed internally by each HappyPlugin instance, but you may override this behavior for better results.

The section on thread pools explains how and when to use this.

Defaults to: null

`verbose: Boolean`

Enable this to log status messages from HappyPack to STDOUT like start-up banner, etc..

Defaults to: true

`verboseWhenProfiling: Boolean`

Enable this if you want HappyPack to still produce its output even when you're doing a webpack --profile run. Since this variable was introduced, HappyPack will be silent when doing a profile build in order not to corrupt any JSON output by webpack (i.e. when using --json as well.)

Defaults to: false

`debug: Boolean`

Enable this to log diagnostic messages from HappyPack to STDOUT. Useful for troubleshooting.

Defaults to: false

How it works

HappyPack sits between webpack and your primary source files (like JS sources) where the bulk of loader transformations happen. Every time webpack resolves a module, HappyPack will take it and all its dependencies and distributes those files to multiple worker "threads".

Those threads are actually simple node processes that invoke your transformer. When the compiled version is retrieved, HappyPack serves it to its loader and eventually your chunk.

Using multiple instances

It's possible to define multiple HappyPack plugins for different types of sources/transformations. Just pass in a unique id for each plugin and make sure you pass it their loaders. For example:

// @file webpack.config.js
exports.plugins = [
  new HappyPack({
    id: 'jsx',
    threads: 4,
    loaders: [ 'babel-loader' ]
  }),

  new HappyPack({
    id: 'styles',
    threads: 2,
    loaders: [ 'style-loader', 'css-loader', 'less-loader' ]
  })
];

exports.module.rules = [
  {
    test: /\.js$/,
    use: 'happypack/loader?id=jsx'
  },

  {
    test: /\.less$/,
    use: 'happypack/loader?id=styles'
  },
]

Now .js files will be handled by the first Happy plugin which will use babel-loader to transform them, while .less files will be handled by the second one using the style loaders.

Shared thread pools

Normally, each HappyPack plugin you create internally creates its own threads which are used to run the loaders. However, if you're using more than one HappyPack plugin it can be more optimal to create a thread pool yourself and then configure the plugins to share that pool, minimizing the idle time of threads within it.

Here's an example of using a custom pool of 5 threads that will be shared between loaders for both JS and SCSS/LESS/whatever sources:

// @file: webpack.config.js
var HappyPack = require('happypack');
var happyThreadPool = HappyPack.ThreadPool({ size: 5 });

module.exports = {
  // ...
  plugins: [
    new HappyPack({
      id: 'js',
      threadPool: happyThreadPool,
      loaders: [ 'babel-loader' ]
    }),

    new HappyPack({
      id: 'styles',
      threadPool: happyThreadPool,
      loaders: [ 'style-loader', 'css-loader', 'less-loader' ]
    })
  ]
};

Benchmarks

For the main repository I tested on, which had around 3067 modules, the build time went down from 39 seconds to a whopping ~10 seconds.

Here's a rundown of the various states the build was performed in:

Elapsed (ms)	Happy?	Using DLLs?
39851	NO	NO
37393	NO	YES
14605	YES	NO
13925	YES	NO
11877	YES	NO
9228	YES	YES

The builds above were run under Linux on a machine with 12 cores.

Changes

See ./CHANGELOG.md.

FAQ

Does it work with webpack 2?

As of version 3.0.3, it does to a certain extent. You can look at the pending issues to see if any of those affect you.

If you come across an issue that is exclusive to webpack 2, a fix has to be provided by the community (or you) as the author currently has no plans for providing webpack 2 support.

Does it work with TypeScript?

The short answer is: yes, it finally does! The longer answer is that you need to use ts-loader in "transpiling-only" mode then use the special plugin fork-ts-checker-notifier-webpack-plugin to perform static type checking.

More information can be found in the ts-loader "happypack mode" section and you can refer to the example that shows this in action.

Big thanks to @johnnyreilly, @aindlq, @piotr-oles, @abergs and many others for making this work.

Does it work with loader XYZ?

We're keeping track of loader support in this wiki page. Some loaders may require extra configuration to make them work.

If the loader you're trying to use isn't listed there, you can refer to this wiki page to see which loader APIs are supported. If your loader uses any API that is NOT supported, chances are that it will not work with HappyPack.

As a general rule, any loader that accepts "functions" in options will not work unless it also accepts reading those options from a file, like babel-loader does with .babelrc and postcss-loader too.

Does it work under Windows?

Yes, as of version 4.0.0 it should. If you come across issues using the plugin on Windows, feel free to open a ticket.

License (MIT)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

tangxuantao/happypack