Svelte 5 Web Component

Create a second vite config

vite.webcomponents.config.ts

import { defineConfig } from 'vite';
import { svelte } from '@sveltejs/vite-plugin-svelte';

export default defineConfig({
	plugins: [
		svelte({
			compilerOptions: {
				customElement: true
			}
		})
	],
	build: {
		lib: {
			entry: 'src/lib/web-components.js',
			name: 'MyWebComponents',
			fileName: 'my-web-components',
			formats: ['iife']
		},
		rollupOptions: {
			output: {
				inlineDynamicImports: true
			}
		},
		cssCodeSplit: false,
		outDir: 'dist-webcomponents'
	}
});

Modify package.json to include new build script

package.json

{
	"scripts": {
		"build:webcomponents": "vite build --config vite.webcomponents.config.ts",
	}
}

Create web component

src/lib/Component.wc.svelte

<svelte:options customElement="my-component" />

<script>
    let { name = 'world', children } = $props();
</script>

<h1>Hello {name}!</h1>
{@render children()}

Create entry file for web components

src/lib/web-components.ts

export { default as Component } from './Component.wc.svelte';

Build the web components

pnpm build:webcomponents

Web components will be built to dist-webcomponents.

Use the web component

index.html

<!DOCTYPE html>
<html lang="en">
	<head>
		<script src="dist-webcomponents/my-web-components.iife.js"></script>
	</head>
	<body>
		<my-component name="Svelte"></my-component>
	</body>
</html>