Make working with webpack against large code-bases a happier experience.

In a nutshell:

HappyPack makes webpack builds faster by allowing you to transform multiple files in parallel.

See "How it works" below for more details.

• webpack initial build times are horrifying in large codebases (3k+ modules)
• something that works against both a one-time build (e.g. for a CI) and with persistent processes (--watch during development)

npm install --save-dev happypack

In your webpack.config.js, you need to use the plugin and tell it of the loaders it should use to transform the sources. Note that you must specify the absolute paths for these loaders as we do not use webpack's loader resolver at this point.

var HappyPack = require('happypack');

exports.plugins = [
  new HappyPack({ 
    // loaders is the only required parameter:
    loaders: [ 'babel?presets[]=es2015' ],

    // customize as needed, see Configuration below
  })
];

Now you replace your current JS loaders with HappyPack's (possibly use an env variable to enable HappyPack):

exports.module = {
  loaders: {
    test: /.js$/,
    loader: 'happypack/loader',
    include: [
      // ...
    ],
  }
};

That's it. Now sources that match .js$ will be handed off to happypack which will use the loaders you specified to transform them.

These are the parameters you can pass to the plugin when you instantiate it.

Each loader entry consists of an absolute path to the module that would transform the files and an optional query string to pass to it.

NOTE

HappyPack at this point doesn't work with all webpack loaders as the loader API is not fully ported yet.

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

The "synchronous" loader signature is:

(source: String, map: ?) -> String

source will be the string contents of the file being transformed. The second parameter, map, is currently not supported. In the future, it should point to the input source map for the file - if any.

You can emit both a source and a map using this.callback:

this.callback(null, code, map);

And you can do it asynchronously by calling this.async:

var callback = this.async();
someAsyncRoutine(function() {
  callback(null, code, map);
});

A unique id for this happy plugin. This is used to generate the default cache name and 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 "Using multiple instances" below for more information on that.

Defaults to: "1"

Path to a folder where happy's cache and junk files will be kept. It's safe to remove this folder after a run but not during it!

Defaults to: .happypack/

Whether HappyPack should re-use the compiled version of source files if their contents have not changed since the last compilation time (assuming they have been compiled, of course.)

Recommended!

Defaults to: true

Path to a file where the JSON cache will be saved to disk and read from on successive webpack runs.

Defaults to .happypack/cache--[id].json

An object that is used to invalidate the cache between runs based on whatever variables that might affect the transformation of your sources, like NODE_ENV for example.

You should provide this if you perform different builds based on some external parameters. THIS OBJECT MUST BE JSON-SERIALIZABLE.

Defaults to: {}

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.) Also, if we're using the cache and the compiled versions are indeed cached, the threads will be idle.

Whether we should intercept the process's SIGINT and clean up when it is received. This is needed because webpack's CLI does not expose any hook for cleaning up when it is going down, so it's a good idea to hook into it.

You can turn this off if you don't want this functionality or it gives you trouble.

Defaults to: true

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, find out if they need to be compiled[1], and if they do, it 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.

[1] When HappyPack successfully compiles a source file, it keeps track of its mtime so that it can re-use it on successive builds if the contents have not changed. This is a fast and somewhat reliable approach, and definitely much faster than re-applying the transformers on every build.

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: 'coffeescripts',
    threads: 2,
    loaders: [ 'coffee-loader' ]
  })
];

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

  {
    test: /\.coffee$/,
    loader: 'happypack/loader?id=coffeescripts'
  },
]

Now .js files will be handled by the first Happy plugin which will use babel-loader to transform them, while .coffee files will be handled by the second one using the coffee-loader as a transformer.

Note that each plugin will properly use different cache files as the default cache file names include the plugin IDs, so you don't need to override them manually. Yay!

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 when there was yet no cache. Successive builds now take between 6 and 7 seconds.

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

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

TODO: test against other projects

1.1.4

• Fixed an issue where the cache was being improperly invalidated due to cacheContext not being stored properly (#17, thanks to @blowery)

1.1.3

• Fixed an issue where the initial cache was not being saved properly

1.1.2

• Fixed an issue on old node versions (0.10) with the EventEmitter API (#10)
• Fixed an issue that was breaking the compiler if an invalid threads option was passed (evaluating to NaN)

1.1.1

• Unrecognized and invalid config parameters will cause the process to abort.
• The active version is logged on launch.

1.1.0

• now supporting basic webpack loaders
• dropped the transformer parameter as it's no longer needed
• cache now defaults to true
• now using a forking model utilizing node.js's process.fork() for cleaner threading code

1.0.2

• the loader will now accept IDs that aren't just numbers