Routing requests manually in Node.js - Step-by-Step Execution

Concept Flow - Routing requests manually

Start Server

↓

Receive HTTP Request

↓

Check Request URL

↓

Handle1

↓

Send Response

↓

End

The server starts and waits for requests. When a request comes, it checks the URL path and sends the matching response or a 404 if no match.

Execution Sample

Node.js

const http = require('http');
const server = http.createServer((req, res) => {
  if (req.url === '/hello') {
    res.end('Hello World');
  } else {
    res.statusCode = 404; res.end('Not Found');
  }
});
server.listen(3000);

This code creates a server that responds with 'Hello World' for '/hello' path and 'Not Found' for others.

Execution Table

Step	Request URL	Condition Checked	Condition Result	Action Taken	Response Sent
1	/hello	req.url === '/hello'	true	Send 'Hello World'	'Hello World'
2	/goodbye	req.url === '/hello'	false	Set status 404 and send 'Not Found'	'Not Found'
3	/unknown	req.url === '/hello'	false	Set status 404 and send 'Not Found'	'Not Found'

💡 Requests handled based on URL; unmatched URLs return 404 Not Found.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
req.url	undefined	/hello	/goodbye	/unknown
res.statusCode	200 (default)	200	404	404
res content	empty	'Hello World'	'Not Found'	'Not Found'

Key Moments - 2 Insights

Why does the server send 'Not Found' for URLs other than '/hello'?

Because the condition req.url === '/hello' is false for other URLs, so the else block sets statusCode to 404 and sends 'Not Found' as shown in execution_table rows 2 and 3.

What happens if we forget to call res.end()?

The server will not send the response back properly, causing the client to wait indefinitely. In the code, res.end() finalizes the response, so missing it stops the response from completing.

Visual Quiz - 3 Questions

Look at the execution table, what response is sent when the request URL is '/hello'?

A 'Not Found'

B 'Hello World'

C Empty response

D Error message

💡 Hint

Check the 'Response Sent' column for Step 1 in the execution_table.

At which step does the server set the status code to 404?

A Both Step 2 and Step 3

B Step 1

C Step 3

D Step 2

💡 Hint

Look at the 'Action Taken' and 'res.statusCode' in variable_tracker for Steps 2 and 3.

If we add a new condition for '/goodbye' to send 'Goodbye!', how would the execution table change for Step 2?

A Server crashes

B Condition result remains false and response is 'Not Found'

C Condition result becomes true and response is 'Goodbye!'

D Response is empty

💡 Hint

Think about adding a new if block for '/goodbye' before the else, changing Step 2's action.

Concept Snapshot

Routing requests manually in Node.js:
- Create server with http.createServer
- Check req.url in callback
- Use if/else to match paths
- Send response with res.end()
- Set res.statusCode for errors
- Unmatched paths return 404 Not Found

Full Transcript

This example shows how to handle HTTP requests manually in Node.js. The server listens for requests and checks the URL path. If the path is '/hello', it sends back 'Hello World'. For any other path, it sets the status code to 404 and sends 'Not Found'. The key is to check req.url and respond accordingly. The response must be ended with res.end() to complete the request. This manual routing is the basic way servers decide what to send back based on the URL.