timepiece/node_modules/date-fns/docs/webpack.md

webpack

Removing unused languages from dynamic import

If a locale is imported dynamically, then all locales from date-fns are loaded by webpack into a bundle (~160kb) or split across the chunks. This prolongs the build process and increases the amount of space taken. However, it is possible to use webpack to trim down languages using ContextReplacementPlugin.

Let's assume that we have a single point in which supported locales are present:

config.js:

// `see date-fns/src/locale` for available locales
export const supportedLocales = ["en-US", "de", "pl", "it"];

We could also have a function that formats the date:

const getLocale = (locale) => import(`date-fns/locale/${locale}/index.js`); // or require() if using CommonJS

const formatDate = (date, formatStyle, locale) => {
  return format(date, formatStyle, {
    locale: getLocale(locale),
  });
};

In order to exclude unused languages we can use webpacks ContextReplacementPlugin.

webpack.config.js:

import webpack from 'webpack'
import { supportedLocales } from './config.js'

export default const config = {
  plugins: [
    new webpack.ContextReplacementPlugin(
      /^date-fns[/\\]locale$/,
      new RegExp(`\\.[/\\\\](${supportedLocales.join('|')})[/\\\\]index\\.js$`)
    )
  ]
}

This results in a language bundle of ~23kb .