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');
...

Create React App and Next.js use this solution.

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

Alternatives

If you are looking for the alternatives to moment.js, please see https://github.com/you-dont-need/You-Dont-Need-Momentjs.

References

• http://stackoverflow.com/questions/25384360/how-to-prevent-moment-js-from-loading-locales-with-webpack/37172595
• moment/moment#2373