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

Maintenance mode notice

My interest in the project is fading away mainly because I'm not using JavaScript as much as I was in the past. Additionally, Webpack's native performance is improving and (I hope) it will soon make this plugin unnecessary.

See the FAQ entry about Webpack 4 and thread-loader.

Contributions are always welcome. Changes I make from this point will be restricted to bug-fixing. If someone wants to take over, feel free to get in touch.

Thanks to everyone who used the library, contributed to it and helped in refining it!!!

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.)

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

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' ]
      }
    }
  ]
}

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"

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

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

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

Defaults to: true

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

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

Defaults to: false

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.

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.

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' ]
    })
  ]
};

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:

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

See ./CHANGELOG.md.

Yes. You should use version >= 4.0.1 (of HappyPack).

Short answer: maybe not.

Long answer: there's now a competing add-on in the form of a loader for processing files in multiple threads, exactly what HappyPack does. The fact that it's a loader and not a plugin (or both, in case of H.P.) makes it much simpler to configure. Look at thread-loader and if it works for you - that's great, otherwise you can try HappyPack and see which fares better for you.

YMMV.

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.

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.

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.

See HACKING.md.

Copyright (c) <2015-2017> ahmad@amireh.net

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