+server.js in SvelteKit: What It Is and How It Works

In SvelteKit, a +server.js file defines server-side endpoints that handle HTTP requests like GET or POST. It runs only on the server and lets you write backend logic such as fetching data or processing forms, separate from the UI code.

How It Works

Think of +server.js as the kitchen in a restaurant where all the cooking happens behind the scenes. When a customer (the browser) orders food (makes a request), the kitchen prepares it and sends it back. Similarly, +server.js files handle requests on the server and send responses back to the client.

In SvelteKit, these files live alongside your page files but only run on the server. They export functions named after HTTP methods like GET or POST. When the app receives a request matching that route, SvelteKit calls the corresponding function in +server.js to process it.

This separation keeps your server logic clean and secure, away from the browser, while still tightly integrated with your app’s routing.

Example

This example shows a simple +server.js that responds to a GET request with JSON data.

javascript

export async function GET() {
  return new Response(JSON.stringify({ message: 'Hello from +server.js!' }), {
    headers: { 'Content-Type': 'application/json' }
  });
}

Output

{"message":"Hello from +server.js!"}

When to Use

Use +server.js when you need to handle backend tasks like fetching data from a database, processing form submissions, or calling external APIs securely. It’s perfect for any logic that should not run in the browser for security or performance reasons.

For example, if you build a contact form, you can use +server.js to receive the form data and send an email without exposing your email service credentials to users.

It also helps keep your app organized by separating server code from UI code, making maintenance easier.

Key Points

• +server.js files run only on the server side in SvelteKit.
• They export functions named after HTTP methods like GET, POST, etc.
• Used to handle backend logic such as data fetching, form handling, and API calls.
• Keep sensitive code and secrets away from the browser.
• Integrate seamlessly with SvelteKit’s routing system.

Key Takeaways

+server.js files define server-only endpoints in SvelteKit.

They handle HTTP requests by exporting functions like GET and POST.

Use them to keep backend logic and secrets secure and separate from UI code.

They integrate with SvelteKit routing to respond to requests on matching routes.

Ideal for tasks like data fetching, form processing, and calling external APIs.