Explaining how to optimize the large bundle size of moment.js with webpack
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README.md

How to optimize moment.js with webpack

When you write var moment = require('moment') in your code and pack with webpack, the size of the bundle file gets heavyweight because it includes all locale files.

To optimize the size, the two webpack plugins are available:

  1. IgnorePlugin
  2. ContextReplacementPlugin

Using IgnorePlugin

You can remove all locale files with the IgnorePlugin.

const webpack = require('webpack');
module.exports = {
  //...
  plugins: [
    // Ignore all locale files of moment.js
    new webpack.IgnorePlugin(/^\.\/locale$/, /moment$/),
  ],
};

And you can still load some locales in your code.

const moment = require('moment');
require('moment/locale/ja');

moment.locale('ja');
...

This solution is used in create-react-app.

Using ContextReplacementPlugin

If you want to specify the including locale files in the webpack config file, you can use ContextReplacementPlugin.

const webpack = require('webpack');
module.exports = {
  //...
  plugins: [
    // load `moment/locale/ja.js` and `moment/locale/it.js`
    new webpack.ContextReplacementPlugin(/moment[/\\]locale$/, /ja|it/),
  ],
};

In this case, you don't need load the locale files in your code.

const moment = require('moment');
moment.locale('ja');
...

Measurements

  • webpack: v3.10.0
  • moment.js: v2.20.1
File size Gzipped
Default 266 kB 69 kB
w/ IgnorePlugin 68.1 kB 22.6 kB
w/ ContextReplacementPlugin 68.3 kB 22.6 kB

Bonus

date-fns is an alternative libraly to moment.js. It doesn't need this kind of tricky solution and has more benefits. It's worth considering.

References