Node.js Get Started

In this lesson you install Node.js and run your first programs.

Installing Node.js

Go to the official Node.js website
Download the LTS version for your system
Run the installer and keep the default options (npm is installed with it)

On Linux and macOS, many developers use a version manager such as nvm, which lets you switch between Node.js versions.

Open a terminal and check that it worked:

Example

bash

node -v
npm -v

Output

v24.11.0
11.6.1

Running Your First File

Create a folder node-practice, open it in VS Code, and create app.js:

Example

const shop = "Ayesha's Bakery";
const cakes = 12;
const pricePerCake = 1500;

console.log("Shop:", shop);
console.log("Cakes in stock:", cakes);
console.log("Stock value: Rs", cakes * pricePerCake);

Run it from the terminal in the same folder:

Example

bash

node app.js

Output

Shop: Ayesha's Bakery
Cakes in stock: 12
Stock value: Rs 18000

The REPL

Type node alone to open the REPL (Read, Evaluate, Print, Loop). You can try JavaScript one line at a time:

Example

bash

node

Example

text

> 25 * 4
100
> "karachi".toUpperCase()
'KARACHI'
> .exit

Use .exit or press Ctrl + C twice to leave.

Useful Global Values

Some values are available in every Node.js file without importing anything:

Name	What it gives you
`console`	Printing: `console.log`, `console.error`, `console.table`
`process`	Information about the running program
`process.argv`	Command-line arguments
`process.env`	Environment variables, like secret keys
`__dirname`	The folder of the current file (CommonJS only)
`setTimeout`, `setInterval`	Timers

Command-Line Arguments

process.argv is an array. The first two items are the path to Node.js and the path to your file; your own arguments come after them.

Example

// greet.js
const name = process.argv[2] || "friend";
const city = process.argv[3] || "Pakistan";

console.log(`Hello ${name} from ${city}!`);

Example

bash

node greet.js Bilal Karachi

Output

Hello Bilal from Karachi!

Environment Variables

Keep passwords and API keys out of your code. Read them from environment variables instead:

Example

const port = process.env.PORT || 3000;
console.log("Server will use port", port);

Recent Node.js versions can load a .env file for you:

Example

bash

node --env-file=.env app.js

Never upload your .env file to GitHub. Add it to .gitignore.

Auto-Restart with --watch

While you are learning, it is useful to rerun the file every time you save:

Example

bash

node --watch app.js

Node.js now restarts the program each time you save a change. Press Ctrl + C to stop. Older projects use a package called nodemon for the same job.

Exiting a Program

A Node.js program ends when there is nothing more to do. A server keeps running because it waits for requests. You can end a program yourself with process.exit():

Example

if (!process.env.API_KEY) {
  console.error("API_KEY is missing");
  process.exit(1);
}

Exit code 0 means success; any other number means an error.

Exercise

Which command runs a file called server.js with Node.js?

npm server.jsrun server.jsnode server.jsjs server.js