Status code usage patterns in Node.js - Mini Project: Build & Apply

Status Code Usage Patterns in Node.js

📖 Scenario: You are building a simple Node.js server that responds to client requests with appropriate HTTP status codes.This helps clients understand if their request was successful or if there was an error.

🎯 Goal: Create a Node.js server using the http module that sends different status codes based on the request URL.You will practice setting status codes like 200, 404, and 500 correctly.

📋 What You'll Learn

Create a basic HTTP server using Node.js http module

Add a variable to hold the success status code 200

Use an if-else statement to send status code 200 for the root URL and 404 for unknown URLs

Add a final else block to send status code 500 for server errors

💡 Why This Matters

🌍 Real World

Web servers must send correct HTTP status codes so browsers and clients know how to handle responses.

💼 Career

Understanding status codes is essential for backend developers and anyone working with web APIs or servers.

1

Create a basic HTTP server

Create a Node.js HTTP server using http.createServer and assign it to a variable called server. The server should respond with status code 200 and the text 'Hello World' for any request.

Node.js

const http = require('http');

// Your code here

Hint

Use http.createServer and set res.statusCode = 200 inside the callback.

2

Add a status code variable

Add a variable called successCode and set it to 200. Use this variable to set the response status code instead of the number directly.

Node.js

const http = require('http');

// Your code here
const server = http.createServer((req, res) => {
    res.statusCode = successCode;
    res.setHeader('Content-Type', 'text/plain');
    res.end('Hello World');
});

Hint

Create const successCode = 200; before the server and use it in res.statusCode.

3

Send 200 for root and 404 for others

Inside the server callback, use if (req.url === '/') to send status code successCode with 'Hello World'. Use else to send status code 404 with 'Not Found'.

Node.js

const http = require('http');

const successCode = 200;

const server = http.createServer((req, res) => {
    // Your code here
});

Hint

Use if (req.url === '/') to check the URL and set status codes accordingly.

4

Add 500 status code for errors

Update the logic: change the existing else to else if (req.url === '/notfound') to send status code 404 and 'Not Found' for that specific URL. Then add a final else block to send status code 500 and 'Server Error' for all other cases. This simulates distinguishing specific client errors from server errors.

Node.js

const http = require('http');

const successCode = 200;

const server = http.createServer((req, res) => {
    // Your code here
});

Hint

Change the existing else to else if (req.url === '/notfound') and add a new else block for status code 500.

Practice

1. What does the HTTP status code 200 generally indicate in a Node.js response?

easy

A. The client made a bad request with invalid syntax.

B. The request was successful and the server returned the requested data.

C. The requested resource was not found on the server.

D. The server encountered an internal error.

Solution

1. Step 1: Understand HTTP status codes

   HTTP status codes communicate the result of a client's request to the server.

2. Step 2: Identify the meaning of 200

   Status code 200 means the request succeeded and the server sent back the expected data.

3. Final Answer:

   The request was successful and the server returned the requested data. -> Option B

4. Quick Check:

   200 = Success [OK]

Hint: 200 means success, data sent back properly [OK]

Common Mistakes:

• Confusing 200 with error codes like 400 or 500
• Thinking 200 means resource not found
• Mixing up client and server error codes

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

easy

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

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

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

D. res.setStatus(404).send('Not Found');

Solution

1. Step 1: Recall Express response methods

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

2. Step 2: Check method correctness

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

3. Final Answer:

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

4. Quick Check:

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

Hint: Use res.status(code) before sending response [OK]

Common Mistakes:

• Using non-existent methods like res.code or res.setStatus
• Passing status code as second argument to send
• Confusing sendStatus with status

3. Consider this Express code snippet:

app.get('/data', (req, res) => {
  if (!req.query.id) {
    return res.status(400).send('Missing id');
  }
  res.status(200).send('Data for ' + req.query.id);
});

What status code will the server respond with if the client calls /data without an id query parameter?

medium

A. 400

B. 404

C. 200

D. 500

Solution

1. Step 1: Analyze the condition for missing id

   The code checks if req.query.id is missing and returns status 400 with message 'Missing id'.

2. Step 2: Determine response when id is missing

   If id is absent, the server responds immediately with status 400 (bad request).

3. Final Answer:

   400 -> Option A

4. Quick Check:

   Missing required data = 400 [OK]

Hint: Missing required input usually means 400 Bad Request [OK]

Common Mistakes:

• Assuming 404 means missing query parameter
• Thinking 200 is always returned
• Confusing 500 server error with client error

4. You have this Express route:

app.post('/submit', (req, res) => {
  if (!req.body.name) {
    res.sendStatus(422);
  }
  res.status(201).send('Created');
});

What is the problem with this code?

medium

A. It should use res.status(400) instead of 422.

B. The status code 422 is not valid in HTTP.

C. The res.status(201) should come before the if block.

D. It sends two responses if name is missing, causing an error.

Solution

1. Step 1: Check response flow when name is missing

   If !req.body.name is true, res.sendStatus(422) sends a response but code continues.

2. Step 2: Identify double response issue

   After sending 422, the code still calls res.status(201).send('Created'), causing an error because response was already sent.

3. Final Answer:

   It sends two responses if name is missing, causing an error. -> Option D

4. Quick Check:

   Send response once per request [OK]

Hint: Return after sending response to avoid double sends [OK]

Common Mistakes:

• Not returning after sending a response
• Confusing 422 with invalid status code
• Thinking order of status calls matters without return

5. You want to create an Express route that returns a JSON error with status 403 if the user is not authorized, and status 200 with data if authorized. Which code snippet correctly implements this pattern?

hard

A. app.get('/secret', (req, res) => {
if (!req.user) {
res.status(403).json({ error: 'Forbidden' });
}
res.status(200).json({ data: 'Secret info' });
});

B. app.get('/secret', (req, res) => {
if (!req.user) {
res.sendStatus(403);
} else {
res.sendStatus(200).json({ data: 'Secret info' });
}
});

C. app.get('/secret', (req, res) => {
if (!req.user) {
return res.status(403).json({ error: 'Forbidden' });
}
res.status(200).json({ data: 'Secret info' });
});

D. app.get('/secret', (req, res) => {
if (!req.user) {
res.status(403).send('Forbidden');
}
res.status(200).send('Secret info');
});

Solution

1. Step 1: Check response flow for unauthorized user

   app.get('/secret', (req, res) => { if (!req.user) { return res.status(403).json({ error: 'Forbidden' }); } res.status(200).json({ data: 'Secret info' }); }); uses return after sending 403 JSON error, preventing further code execution.

2. Step 2: Confirm authorized user response

   It sends status 200 with JSON data correctly if user exists.

3. Final Answer:

   app.get('/secret', (req, res) => { if (!req.user) { return res.status(403).json({ error: 'Forbidden' }); } res.status(200).json({ data: 'Secret info' }); }); -> Option C

4. Quick Check:

   Return after error response to avoid double sends [OK]

Hint: Use return after error response to stop execution [OK]

Common Mistakes:

• Not returning after sending error response
• Using sendStatus with json chaining incorrectly
• Sending plain text instead of JSON for API