GET, POST, PUT, DELETE handlers in Svelte - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of a GET handler in Svelte?

A GET handler retrieves data from the server and sends it back to the client. It is used to fetch information without changing anything on the server.

beginner

How does a POST handler differ from a GET handler?

A POST handler sends data from the client to the server to create or update resources. Unlike GET, POST changes data on the server.

intermediate

What is the role of a PUT handler in Svelte?

A PUT handler updates an existing resource on the server with new data sent from the client. It replaces the entire resource.

beginner

Explain what a DELETE handler does.

A DELETE handler removes a resource from the server. It tells the server to delete the specified data.

intermediate

In SvelteKit, where do you define GET, POST, PUT, DELETE handlers?

You define these handlers in a +server.js or +server.ts file inside the route folder. Each handler is an exported function named GET, POST, PUT, or DELETE.

Which HTTP method is used to fetch data without changing the server state?

A GET

B POST

C PUT

D DELETE

GET requests retrieve data and do not modify server data.

Which handler would you use to create a new resource on the server?

A GET

B PUT

C POST

D DELETE

POST is used to send data to create new resources.

What does a PUT handler do in SvelteKit?

A Deletes a resource

B Fetches data

C Creates a new resource

D Updates an existing resource

PUT replaces or updates an existing resource with new data.

Where do you place HTTP method handlers in a SvelteKit project?

A In +page.svelte files

B In +server.js or +server.ts files

C In app.html

D In static assets folder

Handlers are defined in +server.js or +server.ts files inside route folders.

Which HTTP method should you use to remove data from the server?

A DELETE

B POST

C PUT

D GET

DELETE requests remove resources from the server.

Describe how you would implement a POST handler in SvelteKit to save user data.

Think about reading data from the request and sending back a confirmation.

Explain the difference between GET and PUT handlers in SvelteKit with examples.

Consider what each method does to the server data.

Practice

1. In SvelteKit, what is the main purpose of a GET handler in a route's +server.js file?

easy

A. To update existing data on the server

B. To delete data from the server

C. To fetch and return data when the route is requested

D. To send data to the server without expecting a response

Solution

1. Step 1: Understand the role of HTTP methods

   GET requests are used to retrieve data from a server without changing it.

2. Step 2: Apply this to SvelteKit handlers

   The GET handler in +server.js responds to GET requests by returning data to the client.

3. Final Answer:

   To fetch and return data when the route is requested -> Option C

4. Quick Check:

   GET handler fetches data = B [OK]

Hint: GET handlers always return data for reading [OK]

Common Mistakes:

• Confusing GET with POST or PUT for data updates
• Thinking GET modifies server data
• Assuming GET sends data without response

2. Which of the following is the correct syntax to define a POST handler in SvelteKit's +server.js file?

easy

A. export async function POST({ request }) { return new Response('ok'); }

B. export async function post(request) { return new Response('ok'); }

C. export function Post(request) { return 'ok'; }

D. async function POST() { return 'ok'; }

Solution

1. Step 1: Recall SvelteKit handler naming conventions

   Handlers must be exported async functions named in uppercase: GET, POST, PUT, DELETE.

2. Step 2: Check parameter and return type

   The function receives an object with a request property and returns a Response object.

3. Final Answer:

   export async function POST({ request }) { return new Response('ok'); } -> Option A

4. Quick Check:

   Correct handler syntax = A [OK]

Hint: Use uppercase method names and destructured params [OK]

Common Mistakes:

• Using lowercase function names like 'post'
• Not exporting the function
• Returning plain strings instead of Response objects

3. Given this SvelteKit PUT handler in +server.js:

export async function PUT({ request }) {
  const data = await request.json();
  return new Response(JSON.stringify({ updated: data.id }), { status: 200 });
}

What will be the response body if the client sends {"id": 42} in the request body?

medium

A. undefined

B. {"id":42}

C. 42

D. {"updated":42}

Solution

1. Step 1: Parse JSON from request

   The handler reads JSON from the request body, so data = { id: 42 }.

2. Step 2: Return JSON with updated id

   The response body is JSON stringified object with key 'updated' and value data.id (42).

3. Final Answer:

   {"updated":42} -> Option D

4. Quick Check:

   Response JSON includes updated id = D [OK]

Hint: PUT returns updated data wrapped in JSON [OK]

Common Mistakes:

• Returning original data instead of updated key
• Not stringifying JSON response
• Confusing response body with request body

4. Identify the error in this DELETE handler code snippet:

export async function DELETE(request) {
  const id = await request.json().id;
  return new Response(`Deleted ${id}`, { status: 200 });
}

medium

A. The function parameter should be destructured to get request

B. Cannot await request.json().id directly; must await request.json() first

C. DELETE handlers cannot return Response objects

D. Missing export keyword before function

Solution

1. Step 1: Analyze request.json() usage

   request.json() returns a Promise for the parsed body; you must await it fully before accessing properties.

2. Step 2: Identify incorrect await usage

   Code tries to await request.json().id directly, which is invalid; must await request.json() first, then access .id.

3. Final Answer:

   Cannot await request.json().id directly; must await request.json() first -> Option B

4. Quick Check:

   Await full JSON before property access = C [OK]

Hint: Await request.json() fully before accessing properties [OK]

Common Mistakes:

• Trying to await a property of a Promise
• Not destructuring the parameter (optional but recommended)
• Thinking DELETE handlers can't return Response

5. You want to create a SvelteKit API route that updates a user's name using a PUT handler and returns the updated user object. Which code snippet correctly implements this behavior?

hard

A. export async function PUT({ request }) {
const user = await request.json();
user.name = user.name.toUpperCase();
return new Response(JSON.stringify(user), { status: 200 });
}

B. export async function PUT(request) {
const user = await request.json();
user.name = user.name.toUpperCase();
return user;
}

C. export async function put({ request }) {
const user = await request.json();
user.name = user.name.toUpperCase();
return new Response(JSON.stringify(user));
}

D. export async function PUT({ request }) {
const user = request.json();
user.name = user.name.toUpperCase();
return new Response(JSON.stringify(user), { status: 200 });
}

Solution

1. Step 1: Confirm correct function signature and export

   The handler must be exported async function named PUT with destructured { request } parameter.

2. Step 2: Await request.json() and modify data

   Await the JSON body, then update the user.name property correctly.

3. Step 3: Return a Response with JSON string and status

   Return new Response with JSON stringified user and status 200.

4. Final Answer:

   export async function PUT({ request }) { const user = await request.json(); user.name = user.name.toUpperCase(); return new Response(JSON.stringify(user), { status: 200 }); } -> Option A

5. Quick Check:

   Proper async PUT handler with Response = A [OK]

Hint: Use uppercase function name, await JSON, return Response [OK]

Common Mistakes:

• Not awaiting request.json()
• Using lowercase function name 'put'
• Returning raw object instead of Response