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Your First Node.js Program

Create a project folder, write and run your first Node.js script, pass it input, use a built-in module and learn to read error messages.

Bishal Biswas

Bishal Biswas

Self Learner

Published on: October 25, 2026
Beginner Topic

What you are about to do

You will write a small JavaScript file, then ask Node to run it. That is all a Node program is: a text file of JavaScript plus the node command.

Think of it like leaving a note of instructions for a house-sitter. You write the note (your .js file), hand it over (node hello.js), and they follow it from top to bottom.

You need Node installed. If node --version does not print a version yet, go back to Installing Node.js LTS and Version Managers.

Step 1: make a project folder

Every Node project lives in its own folder. Open a terminal and run:

mkdir hello-node
cd hello-node
  • mkdir (make directory) creates a folder called hello-node.
  • cd (change directory) moves your terminal into it.

Every command you type now runs inside that folder. That matters, because Node looks for your file in the current folder.

Tip: Use a code editor rather than Notepad or TextEdit. VS Code is free, works on every operating system, and understands JavaScript. Open the folder with File, Open Folder.

Step 2: write the program

Create a file called hello.js inside hello-node with one line:

// hello.js
console.log('Hello, Node!');

Save the file. Forgetting to save is the most common reason a beginner’s change “does nothing”.

Step 3: run it

Back in the terminal, type:

node hello.js
Hello, Node!

That is your first Node program. Here is what happened:

  1. The node command started.
  2. It read hello.js from the current folder.
  3. It ran the code from top to bottom, printing the message to the terminal.
  4. With nothing left to do, it exited and gave you your prompt back.

Note: You can leave off the .js ending: node hello also works, because Node tries adding .js for you. Writing the full name is clearer, so this course always does.

Doing a little more

A Node file can hold any JavaScript you already know. Replace the contents of hello.js with this:

// hello.js
const books = ['Dune', 'Emma', 'Beloved'];

function describe(list) {
  return `You have ${list.length} books. The first is ${list[0]}.`;
}

console.log(describe(books));
console.log('Upper case:', books.map((title) => title.toUpperCase()));
node hello.js
You have 3 books. The first is Dune.
Upper case: [ 'DUNE', 'EMMA', 'BELOVED' ]

Notice how Node prints arrays with spaces inside the brackets. That is just Node’s display style.

Giving your program input

Programs are more useful when they can take input. When you run a command, any extra words after the file name are passed to your program. They are called command-line arguments.

Node puts them in an array called process.argv. The first two items are the path to node and the path to your file, so your own words start at index 2.

// greet.js
const name = process.argv[2] ?? 'friend'; // ?? means "use 'friend' if nothing was given"
console.log(`Hello, ${name}!`);
node greet.js
node greet.js Ravi
Hello, friend!
Hello, Ravi!

You will learn a much better way to handle arguments in Command-line Arguments with util.parseArgs.

Using a built-in module

Node comes with built-in modules: ready-made toolboxes for files, the operating system, networking and more. You load one with import.

Create about-me.mjs:

// about-me.mjs
import os from 'node:os';

console.log('Your username is', os.userInfo().username);
console.log('Your computer has', os.cpus().length, 'CPU cores');
node about-me.mjs
Your username is asha
Your computer has 8 CPU cores

Two new things here:

  • The node: prefix says “this is a built-in module, not something downloaded”.
  • The file ends in .mjs, not .js. The m stands for module. It tells Node this file uses the modern import syntax. You will learn the full story, and how to use import in .js files, in CommonJS vs ES Modules.

Writing a file

Now for something a web page could never do. This script creates a real file on your disk:

// save-note.mjs
import { writeFile, readFile } from 'node:fs/promises';

await writeFile('note.txt', 'Buy milk and bread');
const text = await readFile('note.txt', 'utf8');

console.log('Saved and read back:', text);
node save-note.mjs
Saved and read back: Buy milk and bread

Look in your hello-node folder: there is now a note.txt file. await waits for the slow disk work to finish before moving on. In .mjs files you can use await at the top level, outside any function. Reading and Writing Files with fs/promises covers files properly.

Reading an error message

Mistakes are normal. What matters is reading the message Node gives you. Create oops.js with a deliberate typo:

// oops.js
const name = 'Asha';
consol.log('Hello', name);
node oops.js
/Users/asha/hello-node/oops.js:3
consol.log('Hello', name);
^

ReferenceError: consol is not defined
    at Object.<anonymous> (/Users/asha/hello-node/oops.js:3:1)
    ...more "at" lines...

Node.js v24.12.0

Read it from the top:

  • oops.js:3: the file and the line number where things went wrong.
  • The line of code itself, with a ^ pointing at the problem.
  • ReferenceError: consol is not defined: the type of error and a plain description. consol should be console.
  • The at ... lines are the stack trace, the trail of function calls that led here. For small scripts, the first one is usually all you need.

Fix the typo, save, and run it again.

Stopping a program

Most scripts end on their own. Some, like a web server, keep running until you stop them. To stop any running program, press Ctrl + C in the terminal. This works on Windows, macOS and Linux.

Common mistakes

Running from the wrong folder

node hello.js
Error: Cannot find module '/Users/asha/hello.js'

Node looked for hello.js in the current folder and did not find it. Check the path in the message, then cd into the right folder.

Typing JavaScript straight into the terminal

console.log('hi')

The terminal speaks its own command language, not JavaScript, so this fails with a syntax error. Put the code in a file and run node file.js, or start the REPL, which is the next lesson.

Running node with no file name

Typing just node does not run anything. It opens an interactive prompt that looks like >. Press Ctrl + C twice (or Ctrl + D) to leave it. The REPL and Running Scripts explains what this prompt is for.

Quick recap

  • A Node program is a JavaScript file you run with node file.js.
  • Run commands from inside your project folder, or Node will not find the file.
  • console.log prints to the terminal.
  • process.argv holds command-line arguments, starting at index 2.
  • Built-in modules are imported with the node: prefix, such as node:os and node:fs/promises.
  • .mjs files use import and allow top-level await.
  • Error messages tell you the file, the line and what went wrong. Read them from the top.
  • Ctrl + C stops a running program.
script.js

// first-program.mjs: run with "node first-program.mjs Asha"
import os from 'node:os';
import { writeFile, readFile } from 'node:fs/promises';
// --- 1. Plain JavaScript runs top to bottom
const books = ['Dune', 'Emma', 'Beloved'];
console.log(`You have ${books.length} books:`, books.join(', '));
// --- 2. Input from the command line (index 2 onwards is yours)
const name = process.argv[2] ?? 'friend';
const hour = new Date().getHours();
const greeting = hour < 12 ? 'Good morning' : hour < 18 ? 'Good afternoon' : 'Good evening';
console.log(`${greeting}, ${name}!`);
// --- 3. A built-in module tells us about the computer
console.log('Running on', os.platform(), 'with', os.cpus().length, 'CPU cores');
// --- 4. Write a real file, then read it back
const file = 'reading-list.txt';
await writeFile(file, books.map((title, i) => `${i + 1}. ${title}`).join('\n'));
console.log(`\nContents of ${file}:`);
console.log(await readFile(file, 'utf8'));
// --- 5. Errors tell you what went wrong and where
try {
  consol.log('typo!'); // deliberate mistake
} catch (error) {
  console.log(`\nCaught a ${error.name}: ${error.message}`);
}
console.log('Done. Node exits now because nothing is left to do.');

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Installing Node.js LTS and Version Managers

Next

The REPL and Running Scripts

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