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happypack

HappyPack Build Status codecov.io

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.

Motivation

  • 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 continuous builds (i.e. --watch during development)

Usage

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 loaders with HappyPack's loader (possibly use an env variable to enable HappyPack):

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

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.

Configuration

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

loaders: Array.<String|Object{path: String, query: String}>

Each loader entry consists of the name or path of 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.

NOTE

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.

It is possible to omit this value and have HappyPack automatically infer the loaders it should use, see "Inferring loaders" below for more information Inferring loaders has been officially removed as of HappyPack 3.0 and will not be re-introduced (in its previous form, at least) as it has proven to be too costly for the gain it provided.

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 "Using multiple instances" below for more information on that.

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 custom 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.

See "Shared thread pools" below for more information about 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

A diagram showing the flow between HappyPack's components

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.

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: 'coffeescripts',
    threads: 2,
    loaders: [ 'coffee-loader' ]
  })
];
 
exports.module.loaders = [
  {
    test: /\.js$/,
    loaders: [ 'happypack/loader?id=jsx' ]
  },
 
  {
    test: /\.coffee$/,
    loaders: [ '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.

Shared thread pools

Normally, each HappyPlugin instance you create internally manages its own threads which are used to compile sources. However, if you have a number of plugins, it can be more optimal to create a thread pool yourself and then configure the instances 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
    }),
 
    new HappyPack({
      id: 'styles',
      threadPool: happyThreadPool
    })
  ]
};

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
9597 YES YES
6975 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?

It may, and it may not! Official support for webpack 2 will not land until webpack 2 is out of beta status. Until then, IT wouldn't hurt to try but YMMV.

Does it work with loader X or Y?

We're keeping track of known 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.

Does it work under Windows?

There have been a few reports (e.g GH-99 and GH-70) that it does not.

It's difficult for me to confirm or to troubleshoot as I have no access to such an environment. If you do and are willing to help, please do!

License (MIT)

Copyright (c) <2015-2016> ahmad@amireh.net

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.