Response methods and status codes in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the HTTP status code sent by this Express response?

Consider this Express.js code snippet. What status code will the client receive?

Node.js

app.get('/test', (req, res) => {
  res.status(201).send('Created');
});

A 404

B 201

C 200

D 500

💡 Hint

Look at the status method argument.

The res.status(201) sets the HTTP status code to 201, which means 'Created'.

❓ component_behavior

intermediate

What will the response body be for this Express handler?

Given this Express route handler, what will the client see in the response body?

Node.js

app.get('/hello', (req, res) => {
  res.status(200).json({ message: 'Hello World' });
});

A undefined

B Hello World

C {"msg":"Hello World"}

D {"message":"Hello World"}

💡 Hint

Check the method used to send the response.

res.json sends a JSON string of the object, so the client receives {"message":"Hello World"}.

📝 Syntax

advanced

Which option correctly sends a 404 status with a plain text message?

Choose the correct Express.js code to send a 404 status with 'Not Found' text.

A res.send(404, 'Not Found');

B res.sendStatus(404, 'Not Found');

C res.status(404).send('Not Found');

D res.status(404).json('Not Found');

💡 Hint

Check the correct usage of res.status and res.send methods.

Option C correctly sets status 404 and sends plain text. Option C is deprecated syntax. Option C is invalid because sendStatus only takes status code. Option C sends JSON string, not plain text.

🔧 Debug

advanced

Why does this Express handler cause an error?

Identify the error in this Express route handler code.

Node.js

app.get('/error', (req, res) => {
  res.sendStatus(200).send('OK');
});

A res.sendStatus ends the response; calling send after causes an error.

B sendStatus requires two arguments; missing second argument causes error.

C res.sendStatus is not a function; typo in method name.

D send method cannot be chained after status method.

💡 Hint

Check what res.sendStatus returns and if chaining is allowed.

res.sendStatus sends the status and ends the response. Calling send after it causes an error because response is already finished.

🧠 Conceptual

expert

Which status code best fits this scenario in an Express API?

You have an API endpoint that successfully processes a request but does not return any content. Which HTTP status code should you use?

A 204 No Content

B 200 OK

C 202 Accepted

D 404 Not Found

💡 Hint

Think about status codes that indicate success but no response body.

204 means success with no content returned. 200 usually includes content. 202 means accepted but processing not complete. 404 means resource not found.

Practice

1. What does the res.status(404) method do in a Node.js response?

easy

A. Redirects the client to a page named '404'

B. Sends the response body with the text '404'

C. Sets the HTTP status code to 404 (Not Found) for the response

D. Ends the response without sending any data

Solution

1. Step 1: Understand the purpose of res.status()

   This method sets the HTTP status code that tells the browser what happened with the request.

2. Step 2: Identify the meaning of 404 status code

   Status code 404 means 'Not Found', indicating the requested resource does not exist.

3. Final Answer:

   Sets the HTTP status code to 404 (Not Found) for the response -> Option C

4. Quick Check:

   Status code 404 = Not Found [OK]

Hint: Status codes tell browser what happened; 404 means not found [OK]

Common Mistakes:

• Thinking res.status sends the response body
• Confusing status code with redirect
• Assuming res.status ends the response

2. Which of the following is the correct way to send a JSON response with status 200 in Express?

easy

A. res.status(200).json({ message: 'OK' })

B. res.send(200).json({ message: 'OK' })

C. res.json(200, { message: 'OK' })

D. res.status(200).sendJson({ message: 'OK' })

Solution

1. Step 1: Recall Express response chaining

   Use res.status(code) to set status, then call json() to send JSON data.

2. Step 2: Check each option's syntax

   res.status(200).json({ message: 'OK' }) correctly chains status(200) and json(). Others misuse method order or names.

3. Final Answer:

   res.status(200).json({ message: 'OK' }) -> Option A

4. Quick Check:

   Set status then send JSON = res.status(200).json({ message: 'OK' }) [OK]

Hint: Set status first, then call json() to send data [OK]

Common Mistakes:

• Calling send before status
• Using non-existent sendJson method
• Passing status code inside json()

3. What will the following Express code send to the client?

app.get('/test', (req, res) => {
  res.status(201).send('Created');
});

medium

A. A response with status 200 and body 'Created'

B. A response with status 201 and body 'Created'

C. A response with status 201 and no body

D. An error because send() cannot follow status()

Solution

1. Step 1: Understand status and send chaining

   res.status(201) sets status code 201 (Created), then send('Created') sends that text as the response body.

2. Step 2: Confirm behavior of Express response

   Express allows chaining status and send; the response will have status 201 and body 'Created'.

3. Final Answer:

   A response with status 201 and body 'Created' -> Option B

4. Quick Check:

   Status 201 + send text = A response with status 201 and body 'Created' [OK]

Hint: status sets code, send sends body; chaining works [OK]

Common Mistakes:

• Assuming default status 200 is sent
• Thinking send() clears status
• Believing chaining status and send causes error

4. Identify the error in this Express code snippet:

app.get('/redirect', (req, res) => {
  res.send('Redirecting...');
  res.redirect('/new-url');
});

medium

A. Calling res.redirect after res.send causes an error

B. res.redirect should be called before res.send

C. res.send cannot send strings, only JSON

D. No error; this code works fine

Solution

1. Step 1: Understand response flow in Express

   Once res.send() is called, the response is sent and closed.

2. Step 2: Check order of methods

   Calling res.redirect() after res.send() tries to send headers again, causing an error.

3. Final Answer:

   Calling res.redirect after res.send causes an error -> Option A

4. Quick Check:

   Send ends response; redirect after send fails [OK]

Hint: Send or redirect ends response; don't call both [OK]

Common Mistakes:

• Thinking order doesn't matter
• Believing send only works with JSON
• Assuming no error on multiple sends

5. You want to send a JSON response with status 400 and a message 'Invalid input'. Which code correctly does this in Express?

hard

A. res.json(400, { error: 'Invalid input' })

B. res.sendStatus(400).json({ error: 'Invalid input' })

C. res.status(400).send('Invalid input')

D. res.status(400).json({ error: 'Invalid input' })

Solution

1. Step 1: Set the status code correctly

   Use res.status(400) to set the HTTP status to 400 (Bad Request).

2. Step 2: Send JSON response

   Use json() to send the JSON object with the error message.

3. Step 3: Check incorrect options

   res.json(400, { error: 'Invalid input' }) uses wrong method signature (sends 400 as JSON body with status 200); res.status(400).send('Invalid input') sends plain text string (Content-Type text/html) instead of JSON; res.sendStatus(400).json({ error: 'Invalid input' }) ends response with sendStatus before json.

4. Final Answer:

   res.status(400).json({ error: 'Invalid input' }) -> Option D

5. Quick Check:

   Status then json() sends JSON with code [OK]

Hint: Use status() then json() to send JSON with status [OK]

Common Mistakes:

• Passing status code inside json()
• Using send instead of json for JSON data
• Calling sendStatus before json