@preact/preset-vite

An all in one preset for writing Preact apps with the vite bundler.

Features:

• Sets up Hot Module Replacement via prefresh
• Enables Preact Devtools bridge during development
• Aliases React to preact/compat

Installation

First intall the preset package from npm:

npm install --save-dev @preact/preset-vite
# or
yarn add -D @preact/preset-vite

Enhance your vite config with the Preact preset plugin in your vite.config.ts or vite.config.js:

import { defineConfig } from "vite";
import preact from "@preact/preset-vite";

export default defineConfig({
  plugins: [preact()]
});

Options

Options can be passed to our preset plugin via the first argument:

export default defineConfig({
  plugins: [
    preact({ devtoolsInProd: true })
  ]
});

Available options

Option	Type	Default	Description
devtoolsInProd	boolean	false	Inject devtools bridge in production bundle instead of only in development mode
devToolsEnabled	boolean	true	Inject devtools bridge
prefreshEnabled	boolean	true	Inject Prefresh for HMR
reactAliasesEnabled	boolean	true	Aliases react, react-dom to preact/compat
babel	object		See Babel configuration
prerender	object		See Prerendering configuration

Babel configuration

The babel option lets you add plugins, presets, and other configuration to the Babel transformation performed on each JSX/TSX file.

preact({
  babel: {
    presets: [...],
    // Your plugins run before any built-in transform (eg: Fast Refresh)
    plugins: [...],
    // Use .babelrc files
    babelrc: true,
    // Use babel.config.js files
    configFile: true,
  }
})

Prerendering configuration

Option	Type	Default	Description
enabled	boolean	false	Enables prerendering
renderTarget	string	"body"	Query selector for where to insert prerender result in your HTML template
prerenderScript	string	undefined	Absolute path to script containing exported prerender() function. If not provided, will try to find the prerender script in the scripts listed in your HTML entrypoint
additionalPrerenderRoutes	string[]	undefined	Prerendering will crawl your site automatically, but you'd like to prerender some pages that may not be found (such as a /404 page), use this option to specify them
previewMiddlewareEnabled	boolean	false	Vite's preview server as of v5 will not use our prerendered HTML documents automatically. This option enables a middleware that will correct this, allowing you to test the result of prerendering locally
previewMiddlewareFallback	string	/index.html	Fallback path to be used when an HTML document cannot be found via the preview middleware, e.g., /404 or /not-found will be used when the user requests /some-path-that-does-not-exist

To prerender your app, you'll need to do these things:

1. Enable prerendering in the plugin options
2. Specify your render target, if you want the HTML to be inserted anywhere other than the document.body. This location likely should match render(), i.e., render(<App />, document.querySelector('#app')) -> '#app'
3. Create and export a prerender() function from a script. You could add this to your app entrypoint or create a completely separate file for it, either will work. See below for a usage example
4. Specify where your prerender() function is by either a) adding a prerender attribute to the script tag that contains it in your entry HTML (<script prerender src="./my-prerender-script.js">) or b) use the prerenderScript plugin option to specify the location with an absolute path

The plugin simply calls the prerender function you provide so it's up to you to determine how your app should be prerendered. You'll likely want to use preact-render-to-string, or a wrapper around it such as preact-iso's prerender, but whatever you choose, the minimum you'll need to return is an object containing an html property with your HTML string which will then be inserted according to your renderTarget.

Your prerender() function can be asynchronous, so feel free to make HTTP requests to retrieve data (fetch(...)), read files from disk (fs.readFile(...)), or similar things to set up your app.

For a full example implementation, see our demo

import { prerender as ssr } from 'preact-iso';

function App() {
    return <h1>Hello World!</h1>
}

export async function prerender(data) {
    const { html, links: discoveredLinks } = ssr(<App />);

    return {
        html,
        // Optionally add additional links that should be
        // prerendered (if they haven't already been)
        links: new Set([...discoveredLinks, '/foo', '/bar']),
        // Optional data to serialize into a script tag for use on the client:
        //   <script type="application/json" id="preact-prerender-data">{"url":"/"}</script>
        data: { url: data.url },
        // Optionally configure and add elements to the `<head>` of
        // the prerendered HTML document
        head: {
            // Sets the "lang" attribute: `<html lang="en">`
            lang: 'en',
            // Sets the title for the current page: `<title>My cool page</title>`
            title: 'My cool page',
            // Sets any additional elements you want injected into the `<head>`:
            //   <link rel="stylesheet" href="foo.css">
            //   <meta property="og:title" content="Social media title">
            elements: new Set([
                { type: 'link', props: { rel: 'stylesheet', href: 'foo.css' } },
                { type: 'meta', props: { property: 'og:title', content: 'Social media title' } }
            ])
        }
    };
}

License

MIT, see the license file.