Server routes (+server.js) in Svelte - Step-by-Step Execution

Concept Flow - Server routes (+server.js)

Client sends HTTP request

↓

Server route matches URL

↓

+server.js handles request

↓

Process request logic

↓

Send response back to client

↓

Client receives response

This flow shows how a client request is matched to a server route in SvelteKit, handled by +server.js, and then a response is sent back.

Execution Sample

Svelte

export async function GET() {
  return new Response('Hello from server route!');
}

A simple GET server route that responds with a text message.

Execution Table

Step	Action	Input/Condition	Output/Result
1	Client sends GET request to /example	URL: /example	Request received by server
2	Server matches route	Route file: +server.js in /example folder	Route handler selected
3	Execute GET function	No input parameters	Returns Response with body 'Hello from server route!'
4	Server sends response	Response object	Client receives text 'Hello from server route!'
5	Client displays response	Response text	User sees message on screen
6	End	No more steps	Request cycle complete

💡 Request handled and response sent, no further processing needed

Variable Tracker

Variable	Start	After Step 3	Final
request	undefined	GET request object	GET request object
response	undefined	Response('Hello from server route!')	Response('Hello from server route!')

Key Moments - 3 Insights

Why does the server route file have to be named +server.js?

Because SvelteKit uses the +server.js filename to identify server route handlers, as shown in step 2 of the execution_table.

What happens if the GET function does not return a Response?

The server will not send a proper response, causing errors or timeouts. Step 3 shows the GET function must return a Response object.

Can the server route handle other HTTP methods besides GET?

Yes, you can export functions like POST, PUT, DELETE in +server.js to handle those methods, similar to the GET function in step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output of step 3?

A A Response object with text 'Hello from server route!'

B An error message

C Undefined

D A redirect instruction

💡 Hint

Check the 'Output/Result' column in step 3 of the execution_table

At which step does the server decide which route handler to use?

A Step 1

B Step 2

C Step 4

D Step 5

💡 Hint

Look at the 'Action' column to find when route matching happens

If the GET function returned a JSON response instead of text, how would step 3's output change?

A Response with empty body

B Response with text 'Hello from server route!'

C Response with JSON body

D No response returned

💡 Hint

Consider what the GET function returns in step 3 and how changing the body affects the response

Concept Snapshot

Server routes in SvelteKit use +server.js files.
Export functions like GET handle HTTP methods.
Return a Response object to send data.
Server matches URL to route file.
Response is sent back to client.
This enables backend logic inside Svelte apps.

Full Transcript

In SvelteKit, server routes are defined by creating a +server.js file inside a route folder. When a client sends an HTTP request, the server matches the URL to the correct route folder and runs the exported function for the HTTP method, like GET. This function returns a Response object with the data to send back. The server then sends this response to the client, completing the request cycle. This allows you to write backend code alongside your frontend in SvelteKit.