Node.js Installation and Running Basic Scripts

# Check Node.js version
node --version
# or
node -v

# Check npm version
npm --version
# or
npm -v

# Download and install nvm-windows from GitHub
# Then install Node.js
nvm install lts
nvm use lts

# Install nvm
curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.0/install.sh | bash

# Restart terminal or run:
source ~/.bashrc

# Install latest LTS
nvm install --lts
nvm use --lts

# List installed versions
nvm list

# Switch between versions
nvm use 18.17.0

// first-script.js
console.log("Welcome to Node.js!");
console.log("Today is:", new Date().toLocaleDateString());
console.log("Current working directory:", process.cwd());

// Access command line arguments
console.log("Command line arguments:", process.argv);

// Environment variables
console.log("Node environment:", process.env.NODE_ENV || "development");

node first-script.js

// args-demo.js
const args = process.argv.slice(2); // Remove 'node' and script name

if (args.length === 0) {
  console.log("No arguments provided!");
  console.log("Usage: node args-demo.js <name> <age>");
  process.exit(1);
}

const [name, age] = args;
console.log(`Hello ${name}, you are ${age} years old!`);

// Handle optional arguments
if (args[2]) {
  console.log(`Additional info: ${args[2]}`);
}

node args-demo.js John 25 "Software Developer"

node

> console.log('Hello from REPL!');
Hello from REPL!
undefined

> const greeting = 'Hello World';
undefined

> greeting
'Hello World'

> Math.random()
0.8394729834729834

> .help  // Show REPL commands
> .exit  // Exit REPL (or Ctrl+C twice)

// In REPL:
.help     // Show help
.break    // Break out of multi-line expression
.clear    // Clear the context
.exit     // Exit REPL
.save filename    // Save session to file
.load filename    // Load file into session

// calculator.js
function add(a, b) {
  return a + b;
}

function subtract(a, b) {
  return a - b;
}

function multiply(a, b) {
  return a * b;
}

function divide(a, b) {
  if (b === 0) {
    throw new Error("Division by zero is not allowed");
  }
  return a / b;
}

// Get command line arguments
const [operation, num1, num2] = process.argv.slice(2);

if (!operation || !num1 || !num2) {
  console.log("Usage: node calculator.js <operation> <num1> <num2>");
  console.log("Operations: add, subtract, multiply, divide");
  process.exit(1);
}

const a = parseFloat(num1);
const b = parseFloat(num2);

if (isNaN(a) || isNaN(b)) {
  console.log("Please provide valid numbers");
  process.exit(1);
}

try {
  let result;

  switch (operation.toLowerCase()) {
    case "add":
      result = add(a, b);
      break;
    case "subtract":
      result = subtract(a, b);
      break;
    case "multiply":
      result = multiply(a, b);
      break;
    case "divide":
      result = divide(a, b);
      break;
    default:
      console.log("Unknown operation:", operation);
      process.exit(1);
  }

  console.log(`${a} ${operation} ${b} = ${result}`);
} catch (error) {
  console.error("Error:", error.message);
  process.exit(1);
}

node calculator.js add 10 5        # Output: 10 add 5 = 15
node calculator.js multiply 7 8    # Output: 7 multiply 8 = 56
node calculator.js divide 10 0     # Output: Error: Division by zero is not allowed

// file-processor.js
const fs = require("fs");
const path = require("path");

function processFile(filename) {
  // Check if file exists
  if (!fs.existsSync(filename)) {
    console.error(`File '${filename}' not found!`);
    return;
  }

  try {
    // Read file content
    const content = fs.readFileSync(filename, "utf8");

    // Process the content
    const lines = content.split("\n");
    const wordCount = content
      .split(/\s+/)
      .filter((word) => word.length > 0).length;
    const charCount = content.length;

    // Display statistics
    console.log(`\n📄 File: ${filename}`);
    console.log(`📊 Statistics:`);
    console.log(`   Lines: ${lines.length}`);
    console.log(`   Words: ${wordCount}`);
    console.log(`   Characters: ${charCount}`);
    console.log(`   Size: ${fs.statSync(filename).size} bytes`);

    // Show first few lines
    console.log(`\n📖 First 3 lines:`);
    lines.slice(0, 3).forEach((line, index) => {
      console.log(`   ${index + 1}: ${line}`);
    });
  } catch (error) {
    console.error("Error processing file:", error.message);
  }
}

// Get filename from command line
const filename = process.argv[2];

if (!filename) {
  console.log("Usage: node file-processor.js <filename>");
  process.exit(1);
}

processFile(filename);

echo "Hello World\nThis is a test file\nWith multiple lines" > test.txt
node file-processor.js test.txt

# Always specify Node.js version in your project
echo "18.17.0" > .nvmrc

# Team members can then use:
nvm use  # Automatically uses version from .nvmrc

// ❌ Bad - unhandled errors
const result = JSON.parse(userInput);

// ✅ Good - proper error handling
try {
  const result = JSON.parse(userInput);
  console.log("Parsed successfully:", result);
} catch (error) {
  console.error("Invalid JSON:", error.message);
  process.exit(1);
}

// Use appropriate exit codes
process.exit(0); // Success
process.exit(1); // General error
process.exit(2); // Misuse of shell command

// environment.js
const isDevelopment = process.env.NODE_ENV === "development";
const isProduction = process.env.NODE_ENV === "production";
const isTest = process.env.NODE_ENV === "test";

if (isDevelopment) {
  console.log("Running in development mode");
}

// Set environment when running
// NODE_ENV=production node app.js

// main.js - Entry point
function main() {
  try {
    // Your main logic here
    console.log("Application started successfully");
  } catch (error) {
    console.error("Application failed to start:", error.message);
    process.exit(1);
  }
}

// Only run if this file is executed directly
if (require.main === module) {
  main();
}

// Export for testing
module.exports = { main };

node --version          # Check Node.js version
node script.js          # Run a script
node                    # Start REPL
node -e "console.log('Hi')"  # Execute inline code