Creating a basic HTTP server in Node.js - Visual Walkthrough

Concept Flow - Creating a basic HTTP server

Start Node.js

↓

Import http module

↓

Create server with request handler

↓

Server listens on port

↓

Client sends request

↓

Server handles request

↓

Server sends response

↓

Client receives response

↓

End

This flow shows how Node.js starts, creates an HTTP server, listens for requests, handles them, and sends responses back to clients.

Execution Sample

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World');
});

server.listen(3000);

This code creates a simple HTTP server that responds with 'Hello World' to every request on port 3000.

Execution Table

Step	Action	Evaluation	Result
1	Import http module	http module loaded	http object available
2	Create server with request handler	Function passed to createServer	server object created
3	Start server listening on port 3000	server.listen(3000)	Server waits for requests
4	Client sends request	Request received by server	Request object (req) created
5	Server handles request	Execute handler function	Set statusCode=200, set header
6	Server sends response	res.end('Hello World')	Response sent to client
7	Client receives response	Response with 'Hello World'	Client displays 'Hello World'
8	No more requests	Server keeps running	Waiting for next request

💡 Server runs continuously until manually stopped; no exit in normal flow

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 5	After Step 6	Final
http	undefined	http module object	http module object	http module object	http module object	http module object
server	undefined	server object created	server listening	server listening	server listening	server listening
req	undefined	undefined	undefined	request object	request object	undefined
res	undefined	undefined	undefined	response object	response sent	undefined

Key Moments - 3 Insights

Why does the server keep running after sending a response?

Because server.listen keeps the Node.js process alive waiting for more requests, as shown in execution_table step 8.

What happens if we don't call res.end()?

The response never finishes, so the client waits forever. Step 6 shows res.end sends the response and ends it.

Why do we set headers before ending the response?

Headers must be sent before the body. Step 5 sets headers, then step 6 ends response with body.

Visual Quiz - 3 Questions

Look at the execution table, what is the statusCode set to in step 5?

A 200

B 404

C 500

D Undefined

💡 Hint

Check step 5 in execution_table where server handles request and sets statusCode

At which step does the server start listening for requests?

A Step 5

B Step 2

C Step 3

D Step 7

💡 Hint

Look at execution_table step 3 where server.listen is called

If we remove res.end(), what happens to the client response?

A Client receives 'Hello World' anyway

B Client waits forever for response to finish

C Server crashes immediately

D Response is sent but with empty body

💡 Hint

Refer to key_moments explanation about importance of res.end() after step 6

Concept Snapshot

Create HTTP server with http.createServer(handler).
Handler gets request and response objects.
Set statusCode and headers on response.
Call res.end() to send response body.
Start server with server.listen(port).
Server runs continuously until stopped.

Full Transcript

This lesson shows how to create a basic HTTP server in Node.js. First, we import the http module. Then, we create a server using http.createServer and provide a function that handles requests and responses. Inside this function, we set the response status code to 200, set the Content-Type header to text/plain, and end the response with 'Hello World'. We start the server listening on port 3000. When a client sends a request, the server runs the handler, sends the response, and the client receives 'Hello World'. The server keeps running waiting for more requests until manually stopped.