Introduction to Node.js

Learning objectives#

• Explain what Node.js is
• Know what Node.js is good and not so good at
• Run a script with node
• Start a tiny web server

Explanation#

Node.js is a JavaScript runtime built on Chrome’s V8 engine. Instead of browser APIs like document and window, it gives you server APIs: files (fs), networking (http), processes and more.

Node uses non-blocking, event-driven I/O. While it waits for a database or a file, it keeps serving other requests. That makes it efficient for APIs, real-time apps (chat, live dashboards) and tooling.

It is less suited to heavy CPU work such as video encoding or large calculations in the main thread — those block every other request (use worker threads or another service).

npm, Node’s package manager, gives you millions of libraries. Tools you already use — Vite, ESLint, the Angular CLI — are Node programs.

Install the LTS version, then run a file with node app.js. Node 22 can run .js files written as ES modules when package.json has "type": "module".

Syntax#

1node --version        # v22.x
2node hello.js         # run a script
3node                  # interactive REPL (Ctrl+C twice to exit)

Code example: A script and a web server in one file#

1import http from 'node:http';
2

3console.log(`Hello from Node.js ${process.version.split('.')[0]}!`);
4console.log('2 + 3 =', 2 + 3);
5

6const server = http.createServer((req, res) => {
7  res.writeHead(200, { 'Content-Type': 'text/plain' });
8  res.end('Hello from my first Node.js server');
9});
10

11server.listen(3000, async () => {
12  console.log('Server running on http://localhost:3000');
13

14  // Try it from the same script (normally you would open the URL in a browser)
15  const response = await fetch('http://localhost:3000');
16  console.log('Browser would show:', await response.text());
17  server.close();
18});

Hello from Node.js v22!
2 + 3 = 5
Server running on http://localhost:3000
Browser would show: Hello from my first Node.js server

This example is illustrative. Copy or download it and run it in your own environment; the expected output is shown above.

Step-by-step explanation#

1. console.log prints to the terminal, not to a browser console.
2. process.version is a Node-only global with the runtime version.
3. http.createServer receives a function that runs for every request.
4. listen(3000) starts accepting connections on port 3000.
5. fetch (built into Node 18+) calls the server; server.close() lets the script exit.

Real-world use case#

Common mistakes#

Best practices#

• Use the LTS version
• Keep request handlers non-blocking
• Use the node: prefix for built-in modules
• Learn async JavaScript well — Node relies on it

Remember this#

Practice exercise#

1const weekday = new Date().toLocaleDateString('en-IN', { weekday: 'long' });
2console.log(`Today is ${weekday}`);
3console.log(`Script running for ${process.uptime().toFixed(2)} s`);

Mini quiz#

Want more? Practise all Node.js MCQs · Node.js interview questions

Related topics#

My notes#

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