GET, POST, PUT, DELETE handlers in Svelte - Step-by-Step Execution

Concept Flow - GET, POST, PUT, DELETE handlers

Client sends HTTP request

↓

Server receives request

↓

Check HTTP method

↓

Fetch

↓

Send response back to client

The server listens for HTTP requests, checks the method (GET, POST, PUT, DELETE), then runs the matching handler to fetch, create, update, or delete data, and finally sends a response.

Execution Sample

Svelte

import { json } from '@sveltejs/kit';

export async function GET() {
  return json({ message: 'Hello GET' });
}

export async function POST({ request }) {
  const data = await request.json();
  return json({ received: data });
}

This SvelteKit code defines GET and POST handlers that respond with JSON data.

Execution Table

Step	HTTP Method	Request Data	Handler Action	Response Sent
1	GET	None	Return JSON { message: 'Hello GET' }	{ message: 'Hello GET' }
2	POST	{ name: 'Alice' }	Parse JSON, return { received: { name: 'Alice' } }	{ received: { name: 'Alice' } }
3	PUT	{ id: 1, name: 'Bob' }	Update resource with id 1, return confirmation	{ updated: { id: 1, name: 'Bob' } }
4	DELETE	{ id: 1 }	Delete resource with id 1, return confirmation	{ deleted: 1 }
5	PATCH	Any	No handler defined, return 405 Method Not Allowed	405 Method Not Allowed

💡 Execution stops after sending response for each request.

Variable Tracker

Variable	Start	After GET	After POST	After PUT	After DELETE	Final
requestData	undefined	undefined	{ name: 'Alice' }	{ id: 1, name: 'Bob' }	{ id: 1 }	undefined
responseData	undefined	{ message: 'Hello GET' }	{ received: { name: 'Alice' } }	{ updated: { id: 1, name: 'Bob' } }	{ deleted: 1 }	undefined

Key Moments - 3 Insights

Why does the POST handler read request.json() but the GET handler does not?

Because POST requests usually send data in the body, so we parse it with request.json(). GET requests do not have a body, so no parsing is needed. See execution_table rows 1 and 2.

What happens if a request uses an HTTP method without a handler?

The server returns a 405 Method Not Allowed response, as shown in execution_table row 5.

How does the server know which handler to run?

It checks the HTTP method of the incoming request and runs the matching handler function (GET, POST, PUT, DELETE). See concept_flow diagram.

Visual Quiz - 3 Questions

Look at the execution_table, what response is sent for the POST request?

A { message: 'Hello GET' }

B { received: { name: 'Alice' } }

C { updated: { id: 1, name: 'Bob' } }

D 405 Method Not Allowed

💡 Hint

Check execution_table row 2 under Response Sent column.

At which step does the server respond with a 405 error?

A Step 1

B Step 3

C Step 5

D Step 4

💡 Hint

Look for the row with '405 Method Not Allowed' in the Response Sent column.

If the PUT handler was missing, what would happen at step 3?

A Return 405 Method Not Allowed

B Return the GET response

C Return empty response

D Server crashes

💡 Hint

Refer to key_moments about missing handlers and execution_table step 5.

Concept Snapshot

GET, POST, PUT, DELETE handlers in SvelteKit:
- Export async functions named GET, POST, PUT, DELETE
- GET reads no body, returns data
- POST/PUT read request.json() to get data
- DELETE usually uses params or body to identify resource
- If method missing, server returns 405 error
- Handlers return JSON responses with json() helper

Full Transcript

In SvelteKit, you create server route files that export async functions named after HTTP methods: GET, POST, PUT, DELETE. When a client sends a request, the server checks the method and runs the matching function. GET handlers usually return data without reading a body. POST and PUT handlers read JSON data from the request body using request.json(). DELETE handlers remove resources identified by parameters or body data. If a request uses a method without a handler, the server responds with a 405 Method Not Allowed error. Each handler returns a JSON response using the json() helper from '@sveltejs/kit'. This flow ensures the server handles different HTTP methods properly and sends back the right responses.