CommonJS Tree Shaker plugin for WebPack
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README.md

CommonJS Tree Shaker plugin for Webpack

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Fancy shaking logo

Please file an issue if anything is broken.

See common-shake for abstract bundler-independent implementation.

NOTE: webpack version 4 may be needed in order to run this. If you're using webpack 3, please use webpack-common-shake@1.x.

NOTE: Logo is a modified version of webpack's logo

Why?

There are vast amount of CommonJS modules out there. Thus CommonJS Tree Shaking is as important as the ESM module import/export shaking.

How?

This plugin removes unused assignments to exports properties leaving removal of the (presumably) dead code to UglifyJS. If, for example, you had a module:

exports.used = 1;
var tmp = exports.unused = 2;

This plugin will transform it to:

exports.used = 1;
var tmp = 2;

It is up to UglifyJS (or some other optimizer) to decide, whether tmp is used or not and delete it. Luckily it is much simpler for it to do if the uses are not clouded by exporting the values.

Usage

Example webpack.config.js:

const ShakePlugin = require('webpack-common-shake').Plugin;

module.exports = [{
  entry: 'entry.js'
  output: {
    path: 'dist',
    filename: 'output.js'
  },
  plugins: [ new ShakePlugin() ]
}];

Demonstration

See webpack-common-shake-demo for size comparison of output with and without this plugin.

Options

Plugin constructor accepts options object which may have following properties:

const plugin = new ShakePlugin({
  warnings: {
    global: true,
    module: false
  } /* default */,

  // Invoked on every deleted unused property
  onExportDelete: (resource, property) => {},

  // See `Limitations` section for description
  onModuleBailout: (module, bailouts) => { ... },
  onGlobalBailout: (bailouts) => { ... }
});

Limitations

Although, generally this module works and helps removing unused code from the bundles. There are some limitations that may prevent it from running either partially or completely. Some examples are provided below, otherwise please use common sense (or onModuleBailout, onGlobalBailout plugin options).

Some local (partial) bailouts:

  • Dynamic exports exports[Math.random()] = ...
  • Overriding imported vars var a = require('./a'); a.lib; a = require('./b')
  • Using require in unknown way console.log(require('./lib'))
  • Destructuring require dynamically { [prop]: name } = require('./a')
  • Dynamic import var fn = require('./lib')[Math.random()]

Some global (full) bailouts:

  • Dynamic use of require require(Math.random())

This plugin will print some webpack warnings. In any case, bailouts may be obtained programmatically too:

const plugin = new ShakePlugin({
  onModuleBailout: (module, bailouts) => { ... },
  onGlobalBailout: (bailouts) => { ... }
});

Graph

For debugging and inspection purposes a graph in dot format may be obtained using onGraph option:

const plugin = new ShakePlugin({
  onGraph: (graph) => { ... }
});

LICENSE

This software is licensed under the MIT License.

Copyright Fedor Indutny, 2017.

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.