Status code conventions in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding HTTP status codes in Express

Which HTTP status code should you use in Express when a client sends a request with missing required data?

A 404 Not Found

B 200 OK

C 400 Bad Request

D 500 Internal Server Error

💡 Hint

Think about what status code means the client made a bad request.

400 Bad Request means the server cannot process the request due to client error, such as missing data.

❓ component_behavior

intermediate

Express response status for successful resource creation

What status code does Express typically send when a new resource is successfully created?

A 201 Created

B 202 Accepted

C 204 No Content

D 200 OK

💡 Hint

This code means the server created something new.

201 Created indicates that the request was successful and a new resource was created.

📝 Syntax

advanced

Correct usage of status codes in Express response

Which Express code snippet correctly sends a 404 status with a JSON error message?

A res.json(404, { error: 'Not found' });

B res.status(404).json({ error: 'Not found' });

C res.status(404).send({ error: 'Not found' });

D res.sendStatus(404).json({ error: 'Not found' });

💡 Hint

Check the chaining and method usage for setting status and sending JSON.

res.status(404).json(...) sets the status code and sends JSON correctly.

❓ state_output

advanced

Output status code for unauthorized access in Express

What status code will Express send if you use res.status(401).send('Unauthorized')?

Express

app.get('/secret', (req, res) => {
  res.status(401).send('Unauthorized');
});

A 401 Unauthorized with body 'Unauthorized'

B 200 OK with body 'Unauthorized'

C 403 Forbidden with body 'Unauthorized'

D 500 Internal Server Error

💡 Hint

The status code you set is sent as the HTTP response status.

res.status(401) sets the HTTP status to 401 Unauthorized, and send() sends the response body.

🔧 Debug

expert

Identify the error in status code usage

What error occurs when running this Express code snippet?

app.get('/data', (req, res) => {
  res.status(201).send('Created');
  res.status(200).send('OK');
});

Express

app.get('/data', (req, res) => {
  res.status(201).send('Created');
  res.status(200).send('OK');
});

A No error, sends 201 Created

B SyntaxError: Unexpected token

C No error, sends 200 OK

D Error: Cannot set headers after they are sent to the client

💡 Hint

Think about sending multiple responses in one request.

Express throws an error if you try to send more than one response for a single request.

Practice

1. In Express, which status code is conventionally used to indicate a successful GET request?

easy

A. 301 Moved Permanently

B. 404 Not Found

C. 500 Internal Server Error

D. 200 OK

Solution

1. Step 1: Understand HTTP status codes for success

   The status code 200 means the request was successful and the server returned the requested data.

2. Step 2: Match the code to the GET request success

   For a successful GET request, 200 OK is the standard code to indicate success.

3. Final Answer:

   200 OK -> Option D

4. Quick Check:

   Success code for GET = 200 OK [OK]

Hint: 200 means success, use it for successful GET requests [OK]

Common Mistakes:

• Using 404 for success
• Using 500 for client errors
• Confusing 301 with success

2. Which of the following is the correct way to set a 404 status code in Express?

easy

A. res.statusCode = 404; res.send('Not Found')

B. res.sendStatus(200)

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

D. res.code(404).send('Not Found')

Solution

1. Step 1: Recall Express method to set status code

   Express uses res.status(code) to set the HTTP status code before sending a response.

2. Step 2: Verify correct syntax for 404

   res.status(404).send('Not Found') correctly sets status 404 and sends the message.

3. Final Answer:

   res.status(404).send('Not Found') -> Option C

4. Quick Check:

   Use res.status(code) to set status [OK]

Hint: Use res.status(code) before send() to set status [OK]

Common Mistakes:

• Using res.code() which doesn't exist
• Setting res.statusCode directly without chaining
• Using sendStatus(200) for 404

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

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

medium

A. 201 Created

B. 404 Not Found

C. 200 OK

D. 500 Internal Server Error

Solution

1. Step 1: Identify the status code set in the code

   The code uses res.status(201) which sets the HTTP status code to 201.

2. Step 2: Understand the meaning of 201

   Status 201 means the request was successful and a new resource was created.

3. Final Answer:

   201 Created -> Option A

4. Quick Check:

   res.status(201) sends 201 Created [OK]

Hint: res.status(201) means resource created successfully [OK]

Common Mistakes:

• Assuming default 200 status
• Confusing 201 with 404
• Ignoring the status() call

4. You wrote this Express code but clients always get status 200 instead of 400:

app.post('/submit', (req, res) => {
  if (!req.body.name) {
    res.status(400);
    res.send('Name is required');
  }
});

What is the main problem?

medium

A. res.send() must come before res.status()

B. res.status(400) must be followed by return to stop execution

C. 400 is not a valid status code

D. res.status() does not set the status code

Solution

1. Step 1: Analyze the code flow after setting status 400

   res.status(400) sets the status but code continues to run after sending response.

2. Step 2: Understand Express response behavior

   Without return, Express may continue and send default 200 later or cause errors.

3. Final Answer:

   res.status(400) must be followed by return to stop execution -> Option B

4. Quick Check:

   Use return after res.status().send() to stop further processing [OK]

Hint: Add return after res.status().send() to prevent default 200 [OK]

Common Mistakes:

• Not returning after sending response
• Calling res.send() before res.status()
• Thinking 400 is invalid

5. You want to send a 204 No Content status after deleting a resource in Express. Which code snippet correctly does this?

hard

A. res.status(204).send()

B. res.sendStatus(204).send('Deleted')

C. res.status(204).send('Deleted')

D. res.send(204)

Solution

1. Step 1: Understand 204 No Content meaning

   204 means success but no response body should be sent.

2. Step 2: Choose code that sends 204 without content

   res.status(204).send() sends status 204 with empty body, which is correct.

3. Step 3: Identify incorrect options

   res.sendStatus(204).send('Deleted') tries to chain send() after sendStatus(), which is invalid. res.status(204).send('Deleted') sends a body with 204, which breaks the rule. res.send(204) sends 204 as body, not status.

4. Final Answer:

   res.status(204).send() -> Option A

5. Quick Check:

   204 means no content, so send empty response [OK]

Hint: Use res.status(204).send() to send no content response [OK]

Common Mistakes:

• Sending body with 204 status
• Using sendStatus(204).send()
• Sending status code as body