HTTP method handlers (GET, POST) in NextJS - Mini Project: Build & Apply

HTTP Method Handlers (GET, POST) in Next.js

📖 Scenario: You are building a simple Next.js API route that handles user messages. Users can send a message with a POST request, and retrieve all messages with a GET request.

🎯 Goal: Create a Next.js API route that stores messages in memory. Implement a GET handler to return all messages and a POST handler to add a new message.

📋 What You'll Learn

Create an empty array called messages to store message objects

Create a variable called jsonHeaders with the value { 'Content-Type': 'application/json' }

Write an async GET function that returns all messages as JSON with status 200 and jsonHeaders

Write an async POST function that reads JSON from the request, adds the new message to messages, and returns the added message with status 201 and jsonHeaders

💡 Why This Matters

🌍 Real World

API routes in Next.js are used to build backend endpoints for web apps, handling data fetching and updates.

💼 Career

Understanding HTTP method handlers is essential for full-stack development and building RESTful APIs.

1

Create the messages array

Create an empty array called messages to store message objects.

NextJS

# Your code here

Hint

Use const messages = [] to create an empty array.

2

Add JSON headers configuration

Create a constant called jsonHeaders and set it to { 'Content-Type': 'application/json' }.

NextJS

const messages = []
// Your code here

Hint

Use const jsonHeaders = { 'Content-Type': 'application/json' } to set headers.

3

Implement the GET handler

Write an async function called GET that returns a new Response with the JSON string of messages, status 200, and headers jsonHeaders.

NextJS

const messages = []
const jsonHeaders = { 'Content-Type': 'application/json' }

// Your code here

Hint

Use new Response(JSON.stringify(messages), { status: 200, headers: jsonHeaders }) to send the messages.

4

Implement the POST handler

Write an async function called POST that reads JSON from the request using await request.json(), pushes the new message to messages, and returns a new Response with the added message as JSON, status 201, and headers jsonHeaders.

NextJS

const messages = []
const jsonHeaders = { 'Content-Type': 'application/json' }

export async function GET() {
  return new Response(JSON.stringify(messages), { status: 200, headers: jsonHeaders })
}

// Your code here

Hint

Use await request.json() to get the new message, then add it to messages and respond with status 201.

Practice

1. In Next.js API routes, how do you define a handler for a GET request?

easy

A. Define a function named handleGetRequest and call it manually.

B. Export an async function named GET from the route file.

C. Use app.get() inside the route file.

D. Export a function named getHandler from the route file.

Solution

1. Step 1: Understand Next.js route handler naming

   Next.js expects exported async functions named after HTTP methods like GET or POST to handle those requests.

2. Step 2: Identify the correct naming convention

   Only exporting an async function named GET will handle GET requests automatically.

3. Final Answer:

   Export an async function named GET from the route file. -> Option B

4. Quick Check:

   GET handler = async function named GET [OK]

Hint: Name the function exactly GET to handle GET requests [OK]

Common Mistakes:

• Using incorrect function names like getHandler
• Trying to call handlers manually
• Using Express.js style app.get() in Next.js route files

2. Which of the following is the correct syntax to define a POST handler in a Next.js route file?

easy

A. export async function POST(request) { /* code */ }

B. export async function post(request) { /* code */ }

C. export function POST(request) { /* code */ }

D. export async function handlePOST(request) { /* code */ }

Solution

1. Step 1: Check function naming and case sensitivity

   Next.js requires the handler function to be named exactly POST in uppercase to handle POST requests.

2. Step 2: Confirm async keyword usage

   Handler functions should be async to handle asynchronous operations like reading request body.

3. Final Answer:

   export async function POST(request) { /* code */ } -> Option A

4. Quick Check:

   POST handler = async function named POST [OK]

Hint: Use uppercase POST and async keyword for POST handlers [OK]

Common Mistakes:

• Using lowercase 'post' instead of uppercase 'POST'
• Omitting async keyword
• Wrong function names like handlePOST

3. Given this Next.js route handler code, what will be the response to a POST request?

export async function POST(request) {
  const data = await request.json();
  return new Response(JSON.stringify({ message: `Hello, ${data.name}!` }), { status: 200 });
}

And the client sends JSON {"name": "Alice"} in the POST body.

medium

A. SyntaxError due to missing await

B. Empty response with status 200

C. {"message":"Hello, Alice!"}

D. Error: request.json() is not a function

Solution

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

   The code uses await request.json() to parse the JSON body sent by the client, which contains {"name": "Alice"}.

2. Step 2: Construct response with personalized message

   The response JSON string includes the message "Hello, Alice!" using the parsed data.name.

3. Final Answer:

   {"message":"Hello, Alice!"} -> Option C

4. Quick Check:

   POST JSON parsed and response includes name [OK]

Hint: Use await request.json() to read POST JSON body [OK]

Common Mistakes:

• Forgetting to await request.json()
• Returning empty or wrong response
• Misnaming the data property

4. Identify the error in this Next.js route file code for handling GET and POST requests:

export async function GET() {
  return new Response('Hello GET');
}

export function POST(request) {
  const data = request.json();
  return new Response(`Hello ${data.name}`);
}

medium

A. POST handler should be named post in lowercase

B. GET handler should not return Response directly

C. GET handler must accept a request parameter

D. POST handler is missing async keyword and await for request.json()

Solution

1. Step 1: Check POST handler async usage

   The POST handler calls request.json() which returns a promise, so it must be awaited and the function must be async.

2. Step 2: Confirm GET handler and naming

   The GET handler is correctly async and returns a Response; naming and parameters are correct.

3. Final Answer:

   POST handler is missing async keyword and await for request.json() -> Option D

4. Quick Check:

   Async + await needed for request.json() in POST [OK]

Hint: Always use async and await when calling request.json() [OK]

Common Mistakes:

• Not marking POST handler async
• Not awaiting request.json()
• Incorrect handler function names

5. You want to create a Next.js route that responds to both GET and POST requests. The GET returns a JSON list of items, and the POST adds a new item sent in JSON body. Which is the best way to structure your route file?

hard

A. Export async functions named GET and POST; GET returns JSON list; POST reads JSON body and returns updated list.

B. Export a single function handling both GET and POST by checking request.method manually.

C. Use middleware to separate GET and POST logic in different files.

D. Define GET and POST as methods inside a class and export the class.

Solution

1. Step 1: Understand Next.js route handler pattern

   Next.js expects separate exported async functions named after HTTP methods like GET and POST to handle those requests cleanly.

2. Step 2: Structure handlers for each method

   Define GET to return the JSON list and POST to read the JSON body and return the updated list, each in their own async function.

3. Final Answer:

   Export async functions named GET and POST; GET returns JSON list; POST reads JSON body and returns updated list. -> Option A

4. Quick Check:

   Separate GET and POST async functions = clean Next.js pattern [OK]

Hint: Use separate async GET and POST functions for clarity [OK]

Common Mistakes:

• Combining GET and POST in one function
• Using classes or middleware unnecessarily
• Not returning proper JSON responses