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Svelte: Server-Side Rendering with SvelteKit

Svelte: Server-Side Rendering with SvelteKit

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M B A R K
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Server-Side Rendering (SSR) is a technique used to generate HTML on the server, improving initial load time and making applications more SEO-friendly. SvelteKit, the official framework for Svelte, makes SSR simple and powerful. In this article, we’ll cover how to set up SSR in a SvelteKit project, its benefits, and how to integrate it with your Svelte applications.

What is Server-Side Rendering (SSR)?

SSR involves rendering the initial view of your application on the server, sending fully-formed HTML to the client. This results in:

  • Faster initial page load: Users see the content more quickly.

  • SEO improvements: Search engines can index the content since it’s pre-rendered.

  • Reduced load on client-side resources: Less JavaScript is needed to render the initial view.

Setting Up SvelteKit for SSR

Installation

To get started with SvelteKit, you need to install it in your project.

npm init svelte@next my-sveltekit-app
cd my-sveltekit-app
npm install

Project Structure

SvelteKit organizes your application into pages and endpoints. The key parts of your project structure include:

  • src/routes/: This directory holds your pages and API routes.

  • src/lib/: For reusable components and utilities.

Enabling SSR

SSR is enabled by default in SvelteKit, meaning that each page of your application will be server-rendered unless specified otherwise.

Creating a Basic SSR Page

Example: Basic SvelteKit SSR Page

<!-- src/routes/index.svelte -->
<script context="module">
  export async function load() {
    return {
      props: {
        message: 'Welcome to SSR with SvelteKit!'
      }
    };
  }
</script>

<script>
  export let message;
</script>

<h1>{message}</h1>

Explanation:

  • context="module": The load function runs on the server and provides data (like message) to the component before it renders.

  • load Function: This function fetches or computes data that the component will use when it renders.

Fetching Data in SSR

In a real-world application, you’ll often need to fetch data from an API. SvelteKit makes this easy using the load function.

Example: Fetching Data in SSR

<script context="module">
  export async function load() {
    const res = await fetch('https://jsonplaceholder.typicode.com/posts');
    const posts = await res.json();

    return {
      props: {
        posts
      }
    };
  }
</script>

<script>
  export let posts;
</script>

<h1>Blog Posts</h1>
<ul>
  {#each posts as post}
    <li>{post.title}</li>
  {/each}
</ul>

Explanation:

  • Data Fetching: The load function fetches the blog posts from an API, and the data is passed as props to the component.

  • Server-Side Fetching: Since the data is fetched on the server, the HTML is sent to the client with the blog posts already rendered.

SSR and Client-Side Hydration

Once the server sends the initial HTML to the client, SvelteKit “hydrates” the application by attaching the Svelte components to the pre-rendered HTML. This allows your app to behave like a fully interactive Svelte app on the client side.

Example: Adding Interactivity After SSR

<script context="module">
  export async function load() {
    return {
      props: {
        count: 0
      }
    };
  }
</script>

<script>
  export let count;

  function increment() {
    count += 1;
  }
</script>

<h1>Count: {count}</h1>
<button on:click={increment}>Increment</button>

Explanation:

  • Hydration: After the server sends the pre-rendered HTML, the button click handler (increment) is attached to the DOM, making the app interactive.

  • Mixing SSR and Interactivity: You can combine SSR for initial rendering and client-side interactions after the page loads.

Handling Forms and POST Requests

SvelteKit also allows you to handle form submissions and POST requests on the server, making SSR suitable for full-stack applications.

Example: Handling a Form Submission

<!-- src/routes/contact.svelte -->
<script context="module">
  export async function post({ request }) {
    const formData = await request.formData();
    const name = formData.get('name');

    return {
      body: {
        message: `Hello, ${name}!`
      }
    };
  }
</script>

<form method="post">
  <input name="name" placeholder="Your name" />
  <button type="submit">Submit</button>
</form>

{#if message}
  <p>{message}</p>
{/if}

Explanation:

  • post Function: The post function handles form submissions on the server. It processes the form data and returns a response that is rendered on the page.

  • Server-Side Form Handling: SvelteKit provides a full solution for handling form data and actions, both on the client and server.

Benefits of SSR with SvelteKit

  • Improved SEO: SSR makes your content visible to search engines right away.

  • Faster Load Times: The initial page load is faster because the content is already rendered on the server.

  • Scalability: SvelteKit allows you to scale your application with server-side features like data fetching and form handling.

Conclusion

SvelteKit simplifies the process of setting up server-side rendering in your Svelte applications, offering a seamless blend of SSR and client-side interactivity. By leveraging SvelteKit’s powerful SSR features, you can build highly performant, SEO-friendly applications. In the next topic, we’ll explore how to deploy Svelte applications for production.

SvelteJavaScriptFrontend Development