Unhead

Introduction

Unhead has first-class support for Svelte, improving the developer experience and performance of using head tags in your app.

It provides advanced features in comparison to Svelte's in built <svelte:head> component, supporting a more diverse set of use cases from SEO, structured data and script loading.

It's designed to work with any Svelte setup, however this guide assumes you're following a similar structure to the Vite: ssr-svelte-ts template or a Vite SPA.

Demos

Setup

1. Add Dependency

Install @unhead/svelte dependency to your project. The next tag is for v2 of Unhead which is required for Svelte.

bash
pnpm add @unhead/svelte@next

2. Setup Client-Side Rendering

To begin with, we'll import the function to initialize Unhead in our client Svelte app from @unhead/svelte/client.

In Vite this entry file is typically named entry-client.ts. If you're not server-side rendering, you can add this to your main Svelte app entry instead.

src/entry-client.ts
import { createHead, UnheadContextKey } from '@unhead/svelte/client'
import { hydrate } from 'svelte'
import App from './App.svelte'
import './app.css'

// SSR or SPA usage

const unhead = createHead()
const context = new Map()
context.set(UnheadContextKey, unhead)

hydrate(App, {
  target: document.getElementById('app')!,
  context
})
src/main.ts
import { createHead, UnheadContextKey } from '@unhead/svelte/client'
import { mount } from 'svelte'
import App from './App.svelte'
import './app.css'

// SPA usage

const unhead = createHead()
const context = new Map()
context.set(UnheadContextKey, unhead)

const app = mount(App, {
  target: document.getElementById('app')!,
  context,
})

export default app

3. Setup Server-Side Rendering

Serving your app as an SPA? You can skip this step.

Setting up server-side rendering is more complicated as it requires rendering out the tags to the HTML string before sending it to the client.

We'll start with setting up the plugin in the server entry this time. Make sure to import from @unhead/svelte/server instead and add the head in the return object.

src/entry-server.ts
import { createHead, UnheadContextKey } from '@unhead/svelte/server'
import { render as _render } from 'svelte/server'
import App from './App.svelte'

export function render(_url: string) {
  const unhead = createHead()
  const context = new Map()
  context.set(UnheadContextKey, unhead)
  return {
    render: _render(App, {
      context,
    }),
    unhead,
  }
}

Now we need to render out the head tags after Svelte has rendered the app.

Within your server.js file or wherever you're handling the template logic, you need to transform the template data for the head tags using transformHtmlTemplate().

server.ts
import { transformHtmlTemplate } from '@unhead/svelte/server'
// ...

// Serve HTML
app.use('*all', async (req, res) => {
  try {
    // ...

    const rendered = await render(url)
    const html = await transformHtmlTemplate(
      rendered.unhead,
      template
        .replace(`<!--app-head-->`, rendered.head ?? '')
        .replace(`<!--app-html-->`, rendered.html ?? '')
    )

    res.status(200).set({ 'Content-Type': 'text/html' }).send(html)
  }
  catch (e) {
    // ...
  }
})
// ..

4. Your First Tags

Done! Your app should now be rendering head tags on the server and client.

To improve your apps stability, Unhead will now insert important default tags for you.

  • <meta charset="utf-8">
  • <meta name="viewport" content="width=device-width, initial-scale=1">
  • <html lang="en">

You may need to change these for your app requirements, for example you may want to change the default language. Adding tags in your server entry means you won't add any weight to your client bundle.

src/entry-server.ts
import { createHead } from '@unhead/svelte/server'

export function render(_url: string) {
  const head = createHead({
    // change default initial lang
    init: [
      {
        htmlAttrs: { lang: 'en' },
        title: 'Default title',
        titleTemplate: '%s - My Site',
      },
    ]
  })
  const html = `<!-- your html -->`
  return { html, head }
}

For adding tags in your components, you can use the useHead() or useSeoMeta() composables.

App.svelte
<script lang="ts">
  import { useHead, useHead } from '@unhead/Svelte'

  // a.
  useHead({
    title: 'My Awesome Site',
    meta: [
      { name: 'description', content: 'My awesome site description' }
    ]
  })

  // b.
  useSeoMeta({
    title: 'My Awesome Site',
    description: 'My awesome site description'
  })
</script>

For handling reactive input, check out the Reactivity guide.

5. Optional: Auto-Imports

If you're using unplugin-auto-import, you can automatically import the composables.

vite.config.ts
import { autoImports } from '@unhead/svelte'
import AutoImport from 'unplugin-auto-import/vite'

export default defineConfig({
  plugins: [
    AutoImport({
      imports: [
        autoImports,
      ],
    }),
    // ...
  ]
})

Next Steps

Your Svelte app is now setup for head management, congrats! 🎉

You can get started with reactive input for any of the hooks or components:

Or explore some of the optional extras:

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Reactivity

Learn how to handle state changes for head tags in React - from basic state updates to complex data flows.

Reactivity

Learn how to handle state changes for head tags in Svelte.