Simple Script Cut 50% Size Of My React Website

Minh-Phuc Tran on Jan 12, 2021





Hi friends, it's @phuctm97 again. It has been 3 days since my last post, it's my first week at my new job so things have been a little hectic 🤓. Anyway, today article is a very simple but kinda mindblowing script that I did a couple of days ago in my Next.js/React website that cut my site's bundle size from 90kb to a little less than 50kb.





So here is how.

Note: my site is built on top of Next.js (and React).


It's all possible thanks to Preact. Preact is a 3kb alternative implementation of React that provides 100% compatible APIs to React, what it means is that Preact and React are interchangeable but Preact is 4kb whereas React is 40kb. You may be skeptical about whether it's stable, see this list of companies, you'll be confident using it.

So, it's kinda no-brainer to use Preact. However, do keep in mind that the team implementing Preact and React are separate and we aren't sure about what will happen in the future. Also, Preact devtools support is currently quite limited in comparison to React.

So, I figure the best way to use it:

Dev with React and simply swap React and Preact in production bundle, no changes to my dependency tree - I got the best of both worlds, amazing devtools and ecosystem of React and smallest bundle size of Preact for my users 🔥.

Next.js plugin

My website is powered by Next.js, however the same concept is appliable to any other React-based project:

const withPreact = (next = {}) =>
  Object.assign({}, next, {
    webpack(config, options) {
      const { dev, isServer } = options;

      // Use Preact only in client production bundle.
      if (!dev && !isServer) {
        Object.assign(config.resolve.alias, {
          react: "preact/compat",
          "react-dom": "preact/compat",
          "create-react-class": "preact-compat/lib/create-react-class",
          "react-dom-factories": "preact-compat/lib/react-dom-factories",

      if (typeof next.webpack === "function") {
        return next.webpack(config, options);

      return config;

const withMDX = require("@next/mdx")();

module.exports = withPreact(
  // Any other Next.js config. MDX is used as an example for compatibility here.
    pageExtensions: ["ts", "tsx", "mdx"],

You can see that I'm able to use other React-based technologies, too, (MDX in this case).

Also, you'll need to have Preact installed in your package.json:

yarn add preact

Alright, that is it! I'm using it in my website, it's really a no-brainer using Preact this way. Don't worry, I'll let you know whenever my website is not functioning correctly 😉.

Hope it is simple and useful enough to help you save half of your site tomorrow, too!

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