Your First Node.js Program

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

Hello World

Create `hello.js`: ```javascript console.log('Hello, Node.js!'); ```

Run it: ```bash node hello.js # Output: Hello, Node.js! ```

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

Working with Variables

```javascript // 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

```javascript // 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

```javascript // 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

```javascript // 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

```javascript // 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!