mfbx9da4 / nextjs-preactx

Nextjs with Preact X!

A starter template for using Next.js with Preact X!

This starter is ready to be here:

git clone https://github.com/aomkirby123/nextjs-preactX

To migrate from existed project

We need to add next.js and preact

yarn add next preact@10 preact-render-to-string@next preact-ssr-prepass module-alias
yarn add react react-dom --dev

// or using npm
npm install next preact@10 preact-render-to-string@next preact-ssr-prepass module-alias
npm-install react react-dom --save-dev

Note: The lastest preact-render-to-string is version 4 which doesn't support Preact X while preact-render-to-string version 5 supports Preact X but is on the tags of 'next', so we specifiy the version here.

Otherwise, SSR result will be undefined.

Wait, why do we add React here?

Next.js require React and React DOM to run, so we'll use a little trick.

Now create next.config.js as same level as package.json and add:

// next.config.js
const withPreact = (nextConfig = {}) => {
	return Object.assign({}, nextConfig, {
		webpack(config, options) {
			if (!options.defaultLoaders) {
				throw new Error(
				"This plugin is not compatible with Next.js versions below 5.0.0 https://err.sh/next-plugins/upgrade"
				)
			}

			if (options.isServer) {
				config.externals = ["react", "react-dom", ...config.externals]
			}

			config.resolve.alias = Object.assign({}, config.resolve.alias, {
				react: "preact/compat",
				react$: "preact/compat",
				"react-dom": "preact/compat",
				"react-dom$": "preact/compat"
			})

			if (typeof nextConfig.webpack === "function") {
				return nextConfig.webpack(config, options)
			}

			return config
		}
	})
}

module.exports = withPreact()

That's it, You're done!

Wait, what is happening here?

Aliasing React to Preact

Next.js require React and React DOM to be installed to run Next but since we want to use Preact instead, we add Preact then we add React and React DOM as dev dependencies. This make sure that the build process will NOT bundle React and React DOM.

Now we need to alias React and React DOM to Preact instead.

next.config.js

Nextjs provided next.config.js to customize the environment and loader which we can alias React and React DOM to Preact here.

The previous code will alias React and React DOM to Preact and since Preact X, preact-compat is now moved to core as preact/compat.

Custom server with Preact

Note: This is require if you want to use a custom server with Next.js. With default with next.js next.config.js is enough.

We need module-alias to 'alias' React and React DOM to Preact, this will trick Next.js to import Preact instead of React on server since Next.js required React (but we don't actually use them). Now, to alias we need to add this to package.json:

"_moduleAliases": {
    "react": "node_modules/preact/compat",
    "react-dom": "node_modules/preact/compat",
    "react-ssr-prepass": "node_modules/preact-ssr-prepass"
  }

and we also need to alias a custom server. Add this to top of server.js:

require('module-alias/register')

Wait, what is the meaning of this?

On Preact X, preact-compat come with Preact in preact/compat directory, so we defined preact-compat to preact/compat. You might notice that we also alias react-ssr-prepass to preact-ssr-prepass.

The _moduleAliases trick an import from react to preact.

Although, this is enough for running a dev server and production server, but it couldn't be built since Next.js does require React. Now we add React and React DOM to dev-dependencies, this will trick Next.js that we use React (but we actually doesn't use it), since Next.js required React and React DOM, but can only be alias on a custom server.

The reason we need to use custom server is: to ensure that module does alias to Preact correctly otherwise, we are just using React.