Routing requests manually in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when a GET request is made to '/'?

Consider this Node.js server code that manually routes requests. What will the server respond with when a GET request is made to the root path '/'?

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  if (req.method === 'GET' && req.url === '/') {
    res.writeHead(200, { 'Content-Type': 'text/plain' });
    res.end('Home Page');
  } else if (req.method === 'GET' && req.url === '/about') {
    res.writeHead(200, { 'Content-Type': 'text/plain' });
    res.end('About Page');
  } else {
    res.writeHead(404, { 'Content-Type': 'text/plain' });
    res.end('Not Found');
  }
});

server.listen(3000);

A The server responds with 'Not Found' and status 404.

B The server responds with 'About Page' and status 200.

C The server responds with 'Home Page' and status 200.

D The server throws an error and crashes.

💡 Hint

Check the condition that matches the request method and URL.

The code checks if the request method is GET and the URL is '/'. If so, it responds with 'Home Page' and status 200. Other paths or methods get different responses.

📝 Syntax

intermediate

Which option causes a syntax error in manual routing?

Look at these code snippets for routing requests manually in Node.js. Which one will cause a syntax error?

A if (req.method === 'GET' && req.url === '/') { res.end('OK'); }

B if (req.method === 'GET' && req.url === '/about') { res.end('About'); }

C if (req.method === 'POST' && req.url === '/submit') { res.end('Submitted'); }

D if req.method === 'GET' && req.url === '/' { res.end('OK'); }

💡 Hint

Check the syntax of the if statement.

Option D is missing parentheses around the condition in the if statement, causing a syntax error.

🔧 Debug

advanced

Why does this manual routing code always respond with 'Not Found'?

This Node.js server code is supposed to respond with 'Hello' on GET '/' requests, but it always responds with 'Not Found'. What is the cause?

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  if (req.method = 'GET' && req.url === '/') {
    res.writeHead(200, { 'Content-Type': 'text/plain' });
    res.end('Hello');
  } else {
    res.writeHead(404, { 'Content-Type': 'text/plain' });
    res.end('Not Found');
  }
});

server.listen(3000);

A The single '=' assigns 'GET' to req.method, but the condition is always false, so 'Not Found' is sent.

B The single '=' assigns 'GET' to req.method, so the condition is always true and 'Hello' is sent.

C The code throws a runtime error because req.method is read-only.

D The server never starts because of a syntax error.

💡 Hint

Check the operator used in the if condition.

Using '=' assigns 'GET' to req.method, which is truthy, so the condition is always true and 'Hello' is sent. This is a bug because it should use '===' to compare.

❓ state_output

advanced

What is the response when a POST request is made to '/submit'?

Given this manual routing code, what will the server respond with when a POST request is made to '/submit'?

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  if (req.method === 'GET' && req.url === '/') {
    res.writeHead(200, { 'Content-Type': 'text/plain' });
    res.end('Home');
  } else if (req.method === 'POST' && req.url === '/submit') {
    res.writeHead(201, { 'Content-Type': 'text/plain' });
    res.end('Submitted');
  } else {
    res.writeHead(404, { 'Content-Type': 'text/plain' });
    res.end('Not Found');
  }
});

server.listen(3000);

A The server responds with 'Submitted' and status 201.

B The server responds with 'Home' and status 200.

C The server responds with 'Not Found' and status 404.

D The server throws an error because POST is not handled.

💡 Hint

Check the condition that matches POST requests to '/submit'.

The code explicitly checks for POST requests to '/submit' and responds with status 201 and 'Submitted'.

🧠 Conceptual

expert

What is a key limitation of manual routing in Node.js HTTP servers?

When manually routing requests in Node.js using the http module, what is a main limitation compared to using a routing framework?

A Manual routing requires writing repetitive code for each route, making it hard to scale and maintain.

B Manual routing automatically handles query parameters and middleware, which can cause unexpected behavior.

C Manual routing prevents the server from handling concurrent requests efficiently.

D Manual routing forces the use of synchronous code, blocking the event loop.

💡 Hint

Think about code complexity and maintenance.

Manual routing requires explicit if-else checks for each route, leading to repetitive and hard-to-maintain code as the app grows. Frameworks provide cleaner abstractions.

Practice

1. What is the main purpose of checking req.url in a Node.js server without frameworks?

easy

A. To decide how to respond to different request paths

B. To parse the request body automatically

C. To connect to a database

D. To handle user authentication

Solution

1. Step 1: Understand the role of req.url

   req.url contains the path requested by the client, like '/home' or '/about'.

2. Step 2: Purpose of checking req.url

   By checking req.url, the server can decide which content or response to send back.

3. Final Answer:

   To decide how to respond to different request paths -> Option A

4. Quick Check:

   Routing = Check req.url [OK]

Hint: Check req.url to route requests manually [OK]

Common Mistakes:

• Thinking req.url parses request body
• Confusing req.url with database connection
• Assuming req.url handles authentication

2. Which of the following is the correct way to send a plain text response with status 200 in a manual Node.js server?

easy

A. res.status(200).send('Hello');

B. res.writeHead(200, {'Content-Type': 'text/plain'}); res.end('Hello');

C. res.sendStatus(200).send('Hello');

D. res.write(200, 'Hello');

Solution

1. Step 1: Identify correct methods for manual response

   In manual Node.js servers, res.writeHead() sets status and headers, res.end() sends the response body.

2. Step 2: Check each option

   res.writeHead(200, {'Content-Type': 'text/plain'}); res.end('Hello'); uses writeHead and end correctly. The second and third options use Express methods, not native Node.js. res.write(200, 'Hello'); is invalid syntax.

3. Final Answer:

   res.writeHead(200, {'Content-Type': 'text/plain'}); res.end('Hello'); -> Option B

4. Quick Check:

   Manual response = writeHead + end [OK]

Hint: Use writeHead and end to send manual responses [OK]

Common Mistakes:

• Using Express methods in plain Node.js
• Calling res.write without headers
• Incorrect method names like res.sendStatus

3. What will the following Node.js server code output when a client requests /hello?

const http = require('http');
const server = http.createServer((req, res) => {
  if (req.url === '/hello') {
    res.writeHead(200, {'Content-Type': 'text/plain'});
    res.end('Hello World');
  } else {
    res.writeHead(404);
    res.end('Not Found');
  }
});
server.listen(3000);

medium

A. Error: Cannot read property 'writeHead' of undefined

B. Not Found

C. Hello World

D. Server crashes

Solution

1. Step 1: Check the request URL condition

   The code checks if req.url === '/hello'. If true, it sends 'Hello World' with status 200.

2. Step 2: Determine output for '/hello'

   Since the request is '/hello', the first branch runs, sending 'Hello World'.

3. Final Answer:

   Hello World -> Option C

4. Quick Check:

   req.url '/hello' = 'Hello World' [OK]

Hint: Match req.url exactly to send correct response [OK]

Common Mistakes:

• Assuming default response is 'Hello World'
• Confusing 404 and 200 responses
• Expecting server error without syntax issues

4. Identify the error in this manual routing code snippet:

const http = require('http');
const server = http.createServer((req, res) => {
  if (req.url = '/test') {
    res.writeHead(200, {'Content-Type': 'text/plain'});
    res.end('Test page');
  } else {
    res.writeHead(404);
    res.end('Page not found');
  }
});
server.listen(3000);

medium

A. Missing res.end() call

B. server.listen() missing port number

C. Incorrect header format in writeHead

D. Using assignment (=) instead of comparison (===) in if condition

Solution

1. Step 1: Check the if condition syntax

   The condition uses req.url = '/test', which assigns instead of compares. This always evaluates to true.

2. Step 2: Identify correct comparison operator

   It should be req.url === '/test' to compare values properly.

3. Final Answer:

   Using assignment (=) instead of comparison (===) in if condition -> Option D

4. Quick Check:

   Use === for comparison, not = [OK]

Hint: Use === for comparison, not = [OK]

Common Mistakes:

• Confusing assignment and comparison operators
• Forgetting to call res.end()
• Incorrect header object syntax

5. You want to manually route requests to serve JSON data at /data and plain text at /info. Which code snippet correctly implements this?

hard

A. if (req.url === '/data') { res.writeHead(200, {'Content-Type': 'application/json'}); res.end(JSON.stringify({name: 'Node'})); } else if (req.url === '/info') { res.writeHead(200, {'Content-Type': 'text/plain'}); res.end('Information'); } else { res.writeHead(404); res.end('Not Found'); }

B. if (req.url === '/data') { res.end({name: 'Node'}); } else if (req.url === '/info') { res.end('Information'); } else { res.end('Not Found'); }

C. if (req.url === '/data') { res.writeHead(200, {'Content-Type': 'text/plain'}); res.end('{"name":"Node"}'); } else if (req.url === '/info') { res.writeHead(200, {'Content-Type': 'application/json'}); res.end('Information'); } else { res.writeHead(404); res.end('Not Found'); }

D. if (req.url === '/data') { res.writeHead(404); res.end('Not Found'); } else if (req.url === '/info') { res.writeHead(200); res.end('Information'); }

Solution

1. Step 1: Check content types for each route

   For /data, JSON content type 'application/json' is correct. For /info, plain text 'text/plain' is correct.

2. Step 2: Verify response body and headers

   if (req.url === '/data') { res.writeHead(200, {'Content-Type': 'application/json'}); res.end(JSON.stringify({name: 'Node'})); } else if (req.url === '/info') { res.writeHead(200, {'Content-Type': 'text/plain'}); res.end('Information'); } else { res.writeHead(404); res.end('Not Found'); } sets correct headers and uses JSON.stringify for JSON data. Other options misuse content types or omit headers.

3. Final Answer:

   correctly sets headers and responses for both routes -> Option A

4. Quick Check:

   Set correct Content-Type and stringify JSON [OK]

Hint: Set Content-Type and stringify JSON for JSON responses [OK]

Common Mistakes:

• Sending JSON object directly without stringify
• Mixing content types for routes
• Omitting status codes or headers