Why API routes serve backend logic in NextJS - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple API route handler in Next.js.

NextJS

export default function handler(req, res) {
  res.status(200).json({ message: [1] })
}

Drag options to blanks, or click blank then click option'

Aconsole.log('Hello')

BHello from API!

C"Hello from API!"

Dres.send('Hello')

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the string message

Using console.log instead of sending a response

The API route sends a JSON response with a message string. The message must be a string literal inside quotes.

2fill in blank

medium

Complete the code to check the HTTP method in the API route.

NextJS

export default function handler(req, res) {
  if (req.method === [1]) {
    res.status(200).json({ message: "GET request received" })
  } else {
    res.status(405).end()
  }
}

Drag options to blanks, or click blank then click option'

A"GET"

B"POST"

C"PUT"

D"DELETE"

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names without quotes

Checking for the wrong HTTP method

The code checks if the request method is GET to handle GET requests specifically.

3fill in blank

hard

Fix the code in the API route to correctly access JSON data from a POST request.

NextJS

export default async function handler(req, res) {
  if (req.method === "POST") {
    const data = req.[1]
    res.status(200).json({ received: data })
  } else {
    res.status(405).end()
  }
}

Drag options to blanks, or click blank then click option'

Abody

Btext

Cjson

Dparse

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.json() (for app router route handlers)

Calling req.body() as a method

In Next.js API routes, the request body is automatically parsed as JSON. Access it via req.body.

4fill in blank

hard

Fill both blanks to create an API route that responds with a JSON object containing a query parameter.

NextJS

export default function handler(req, res) {
  const name = req.query.[1]
  res.status(200).json({ greeting: `Hello, $[2]!` })
}

Drag options to blanks, or click blank then click option'

Aname

Buser

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for query and greeting

Accessing query parameters incorrectly

Forgetting ${} around the variable in the template literal

The query parameter is accessed as req.query.name, and the greeting interpolates that variable using ${name}.

5fill in blank

hard

Fill all three blanks to create an API route that handles POST requests and returns the posted data with a status message.

NextJS

export default async function handler(req, res) {
  if (req.method === [1]) {
    const data = req.[2]
    res.status(200).json({ status: [3], data })
  } else {
    res.status(405).end()
  }
}

Drag options to blanks, or click blank then click option'

A"POST"

Bbody

C"success"

D"GET"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong HTTP method string

Using req.json() instead of req.body

Wrong status message

The API route checks for POST method, accesses req.body, and returns a success status with the data.

Practice

1. Why do Next.js API routes serve backend logic in a Next.js project?

easy

A. They are used only to style the frontend components.

B. They replace the need for React components in the app.

C. They allow running server-side code like data fetching and secure operations within the same project.

D. They automatically generate static HTML pages.

Solution

1. Step 1: Understand the role of API routes

   API routes in Next.js let you write backend code inside your project to handle tasks like fetching data or processing forms.

2. Step 2: Identify what backend logic means

   Backend logic means code that runs on the server, such as secure operations or database access, which API routes enable.

3. Final Answer:

   They allow running server-side code like data fetching and secure operations within the same project. -> Option C

4. Quick Check:

   API routes = backend logic handler [OK]

Hint: API routes run server code inside Next.js projects [OK]

Common Mistakes:

• Thinking API routes style frontend
• Confusing API routes with React components
• Believing API routes generate static pages

2. Which of the following is the correct way to define a Next.js API route handler?

easy

A. const handler = () => Hello

B. function handler() { return Hello }

C. export function handler() { console.log('Hello') }

D. export default function handler(req, res) { res.status(200).json({ message: 'Hello' }) }

Solution

1. Step 1: Recognize API route syntax

   Next.js API routes export a default function that receives req and res to handle requests and responses.

2. Step 2: Check each option

   export default function handler(req, res) { res.status(200).json({ message: 'Hello' }) } correctly exports a default function with req and res and sends a JSON response. Others either lack export default or return JSX, which is incorrect for API routes.

3. Final Answer:

   export default function handler(req, res) { res.status(200).json({ message: 'Hello' }) } -> Option D

4. Quick Check:

   API route = export default function(req, res) [OK]

Hint: API routes export default function with req, res [OK]

Common Mistakes:

• Returning JSX instead of JSON
• Not exporting default function
• Missing req and res parameters

3. Given this Next.js API route code, what will be the JSON response when a GET request is made?

export default function handler(req, res) {
  if (req.method === 'GET') {
    res.status(200).json({ success: true, data: 'Hello World' })
  } else {
    res.status(405).json({ error: 'Method Not Allowed' })
  }
}

medium

A. {"error":"Method Not Allowed"}

B. {"success":true,"data":"Hello World"}

C. An HTML page with 'Hello World'

D. A runtime error occurs

Solution

1. Step 1: Check request method handling

   The handler checks if the request method is 'GET'. If yes, it sends a 200 status with JSON containing success and data.

2. Step 2: Determine response for GET request

   Since the request is GET, the response will be JSON: {"success":true,"data":"Hello World"} with status 200.

3. Final Answer:

   {"success":true,"data":"Hello World"} -> Option B

4. Quick Check:

   GET request returns success JSON [OK]

Hint: GET method returns success JSON, others error [OK]

Common Mistakes:

• Assuming all methods return success
• Expecting HTML instead of JSON
• Confusing status codes

4. Identify the error in this Next.js API route code:

export default function handler(req, res) {
  if (req.method === 'POST') {
    res.json({ message: 'Data received' })
  } else {
    res.status(405).json({ error: 'Method Not Allowed' })
  }
}

medium

A. No error, code is correct

B. Using res.json instead of res.send

C. Missing status code in the POST response

D. Missing req parameter

Solution

1. Step 1: Review response methods

   In Next.js API routes, res.json() sends a JSON response with a default status code of 200, which is correct and functional.

2. Step 2: Check each option

   The code properly handles POST with res.json() (200 OK implied) and other methods with 405 error. There are no syntax errors, runtime issues, or missing parameters. res.json is the right method for JSON responses.

3. Final Answer:

   No error, code is correct -> Option A

4. Quick Check:

   res.json defaults to 200, code runs correctly [OK]

Hint: res.json() defaults to status 200 [OK]

Common Mistakes:

• Thinking missing explicit status code is an error
• Confusing res.json and res.send
• Forgetting req or res parameters

5. You want to create a Next.js API route that securely processes a form submission only if the request method is POST and the request body contains a non-empty 'email' field. Which code snippet correctly implements this logic?

hard

A. export default function handler(req, res) {
if (req.method === 'POST' && req.body.email) {
res.status(200).json({ message: `Email ${req.body.email} received` })
} else {
res.status(400).json({ error: 'Invalid request' })
}
}

B. export default function handler(req, res) {
if (req.method === 'GET' || !req.body.email) {
res.status(200).json({ message: 'Form processed' })
} else {
res.status(400).json({ error: 'Invalid request' })
}
}

C. export default function handler(req, res) {
if (req.method === 'POST') {
res.status(200).json({ message: 'Form processed' })
} else {
res.status(400).json({ error: 'Invalid request' })
}
}

D. export default function handler(req, res) {
res.status(200).json({ message: 'Form processed' })
}

Solution

1. Step 1: Check method and body content

   The handler must verify the request method is POST and that the 'email' field exists and is not empty in the request body.

2. Step 2: Validate each option

   export default function handler(req, res) { if (req.method === 'POST' && req.body.email) { res.status(200).json({ message: `Email ${req.body.email} received` }) } else { res.status(400).json({ error: 'Invalid request' }) } } correctly checks both conditions and returns a success message with the email. Others either check wrong methods, ignore the email field, or always respond without validation.

3. Final Answer:

   export default function handler(req, res) { if (req.method === 'POST' && req.body.email) { res.status(200).json({ message: `Email ${req.body.email} received` }) } else { res.status(400).json({ error: 'Invalid request' }) } } -> Option A

4. Quick Check:

   POST + email check = export default function handler(req, res) { if (req.method === 'POST' && req.body.email) { res.status(200).json({ message: `Email ${req.body.email} received` }) } else { res.status(400).json({ error: 'Invalid request' }) } } [OK]

Hint: Check method and required fields before responding [OK]

Common Mistakes:

• Not checking request method
• Ignoring required fields in body
• Always returning success without validation