Your First Node.js Program

Let's write real Node.js code. No theory, just practice.

Hello World

Create hello.js:

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

Run it:

node hello.js
# Output: Hello, Node.js!

That's it. You've written Node.js!

Working with Variables

// app.js
const name = 'Alice';
const age = 25;

console.log(`Name: ${name}, Age: ${age}`);

// Arrays and objects work the same
const skills = ['JavaScript', 'Node.js', 'Express'];
const user = { name: 'Bob', role: 'developer' };

console.log(skills);
console.log(user);

Getting User Input

// input.js
const readline = require('readline');

const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

rl.question('What is your name? ', (answer) => {
  console.log(`Hello, ${answer}!`);
  rl.close();
});

Command Line Arguments

// args.js
const args = process.argv.slice(2);

console.log('Arguments:', args);
console.log('First arg:', args[0]);

Run: node args.js hello world

Output:

Arguments: [ 'hello', 'world' ]
First arg: hello

Simple Calculator

// calc.js
const args = process.argv.slice(2);
const num1 = parseFloat(args[0]);
const operator = args[1];
const num2 = parseFloat(args[2]);

let result;
switch (operator) {
  case '+': result = num1 + num2; break;
  case '-': result = num1 - num2; break;
  case '*': result = num1 * num2; break;
  case '/': result = num1 / num2; break;
  default: console.log('Unknown operator'); process.exit(1);
}

console.log(`${num1} ${operator} ${num2} = ${result}`);

Run: node calc.js 10 + 5

Reading a File

// readfile.js
const fs = require('fs');

const content = fs.readFileSync('hello.js', 'utf8');
console.log('File contents:');
console.log(content);

Key Takeaway

Node.js runs JavaScript files with node filename.js. You have access to process.argv for arguments, built-in modules like fs and readline, and all JavaScript features. Start simple, then build up!