Modules & NPM

// math.js - Exporting modules
const add = (a, b) => a + b;
const subtract = (a, b) => a - b;
const multiply = (a, b) => a * b;
const divide = (a, b) => a / b;

// Export individual functions
module.exports.add = add;
module.exports.subtract = subtract;

// Export as an object
module.exports = {
    add,
    subtract,
    multiply,
    divide
};

// app.js - Importing modules
const math = require('./math');

console.log(math.add(5, 3));      // 8
console.log(math.subtract(10, 4)); // 6
console.log(math.multiply(2, 6));  // 12
console.log(math.divide(15, 3));   // 5

// Destructuring imports
const { add, subtract } = require('./math');
console.log(add(5, 3));      // 8
console.log(subtract(10, 4)); // 6

// math.js - ES Module exports
export const add = (a, b) => a + b;
export const subtract = (a, b) => a - b;
export const multiply = (a, b) => a * b;
export const divide = (a, b) => a / b;

// Default export
const calculator = {
    add,
    subtract,
    multiply,
    divide
};

export default calculator;

// app.js - ES Module imports
import { add, subtract, multiply, divide } from './math.js';
import calculator from './math.js';

console.log(add(5, 3));      // 8
console.log(calculator.multiply(2, 6)); // 12

// Dynamic imports
async function loadModule() {
    const math = await import('./math.js');
    console.log(math.add(5, 3));
}

loadModule();

// Initialize a new project
npm init -y

// Install dependencies
npm install express
npm install --save-dev nodemon

// Install specific version
npm install express@4.18.2

// Install globally
npm install -g nodemon

// Remove package
npm uninstall express

// Update packages
npm update

// List installed packages
npm list

// Run scripts
npm start
npm test
npm run dev

// package.json example
{
  "name": "my-node-app",
  "version": "1.0.0",
  "description": "A Node.js application",
  "main": "index.js",
  "scripts": {
    "start": "node index.js",
    "dev": "nodemon index.js",
    "test": "jest"
  },
  "dependencies": {
    "express": "^4.18.2"
  },
  "devDependencies": {
    "nodemon": "^2.0.22"
  }
}

// ES Modules (ESM) - Modern approach
// math.mjs
export const add = (a, b) => a + b;
export const subtract = (a, b) => a - b;

// Default export
export default class Calculator {
    constructor() {
        this.history = [];
    }
    
    calculate(operation, a, b) {
        const result = operation(a, b);
        this.history.push({ operation: operation.name, a, b, result });
        return result;
    }
}

// app.mjs - Importing ES modules
import { add, subtract } from './math.mjs';
import Calculator from './math.mjs';

const calc = new Calculator();
console.log(calc.calculate(add, 5, 3)); // 8

// CommonJS - Traditional approach
// math.js
const add = (a, b) => a + b;
const subtract = (a, b) => a - b;

module.exports = { add, subtract };

// app.js - Importing CommonJS
const { add, subtract } = require('./math');
console.log(add(5, 3)); // 8

// Using both in the same project
// package.json
{
  "type": "module",  // Enable ES modules
  "scripts": {
    "start": "node app.mjs"
  }
}

// package.json with comprehensive scripts
{
  "name": "my-node-app",
  "version": "1.0.0",
  "type": "module",
  "scripts": {
    "start": "node src/index.js",
    "dev": "nodemon src/index.js",
    "test": "jest",
    "test:watch": "jest --watch",
    "test:coverage": "jest --coverage",
    "lint": "eslint src/**/*.js",
    "lint:fix": "eslint src/**/*.js --fix",
    "build": "webpack --mode production",
    "build:dev": "webpack --mode development",
    "clean": "rimraf dist",
    "precommit": "npm run lint && npm run test",
    "deploy": "npm run build && npm run test && pm2 start ecosystem.config.js",
    "logs": "pm2 logs",
    "restart": "pm2 restart all"
  },
  "dependencies": {
    "express": "^4.18.2",
    "cors": "^2.8.5",
    "helmet": "^6.0.1"
  },
  "devDependencies": {
    "nodemon": "^2.0.22",
    "jest": "^29.0.0",
    "eslint": "^8.0.0",
    "webpack": "^5.0.0",
    "rimraf": "^3.0.2",
    "pm2": "^5.0.0"
  }
}

// Custom script example
// scripts/setup.js
import fs from 'fs';
import path from 'path';

const setupProject = () => {
    const dirs = ['src', 'tests', 'docs', 'logs'];
    
    dirs.forEach(dir => {
        if (!fs.existsSync(dir)) {
            fs.mkdirSync(dir, { recursive: true });
            console.log(`Created directory: ${dir}`);
        }
    });
    
    // Create basic files
    const files = {
        'src/index.js': 'console.log("Hello from Node.js!");',
        'tests/index.test.js': 'import { test } from "jest";

test("basic test", () => {
  expect(1 + 1).toBe(2);
});',
        '.gitignore': 'node_modules/
.env
logs/
dist/',
        '.env.example': 'PORT=3000
NODE_ENV=development'
    };
    
    Object.entries(files).forEach(([filePath, content]) => {
        if (!fs.existsSync(filePath)) {
            fs.writeFileSync(filePath, content);
            console.log(`Created file: ${filePath}`);
        }
    });
    
    console.log('Project setup complete!');
};

setupProject();

// Create a comprehensive calculator using modules
// src/calculator/operations.js
export const add = (a, b) => a + b;
export const subtract = (a, b) => a - b;
export const multiply = (a, b) => a * b;
export const divide = (a, b) => {
    if (b === 0) throw new Error('Division by zero');
    return a / b;
};

export const power = (a, b) => Math.pow(a, b);
export const sqrt = (a) => {
    if (a < 0) throw new Error('Square root of negative number');
    return Math.sqrt(a);
};

// src/calculator/history.js
class History {
    constructor() {
        this.operations = [];
    }
    
    add(operation, a, b, result) {
        this.operations.push({
            id: Date.now(),
            operation,
            operands: { a, b },
            result,
            timestamp: new Date().toISOString()
        });
    }
    
    getAll() {
        return this.operations;
    }
    
    getLast(n = 5) {
        return this.operations.slice(-n);
    }
    
    clear() {
        this.operations = [];
    }
    
    export() {
        return JSON.stringify(this.operations, null, 2);
    }
}

export default History;

// src/calculator/validator.js
export const validateNumber = (num) => {
    if (typeof num !== 'number' || isNaN(num)) {
        throw new Error('Invalid number provided');
    }
    return true;
};

export const validateOperation = (op) => {
    const validOps = ['add', 'subtract', 'multiply', 'divide', 'power', 'sqrt'];
    if (!validOps.includes(op)) {
        throw new Error(`Invalid operation: ${op}`);
    }
    return true;
};

// src/calculator/index.js
import * as operations from './operations.js';
import History from './history.js';
import { validateNumber, validateOperation } from './validator.js';

class Calculator {
    constructor() {
        this.history = new History();
    }
    
    calculate(operation, a, b = null) {
        try {
            validateOperation(operation);
            validateNumber(a);
            if (b !== null) validateNumber(b);
            
            let result;
            switch (operation) {
                case 'add':
                    result = operations.add(a, b);
                    break;
                case 'subtract':
                    result = operations.subtract(a, b);
                    break;
                case 'multiply':
                    result = operations.multiply(a, b);
                    break;
                case 'divide':
                    result = operations.divide(a, b);
                    break;
                case 'power':
                    result = operations.power(a, b);
                    break;
                case 'sqrt':
                    result = operations.sqrt(a);
                    break;
            }
            
            this.history.add(operation, a, b, result);
            return result;
            
        } catch (error) {
            console.error('Calculation error:', error.message);
            throw error;
        }
    }
    
    getHistory() {
        return this.history.getAll();
    }
    
    getLastOperations(n = 5) {
        return this.history.getLast(n);
    }
    
    clearHistory() {
        this.history.clear();
    }
    
    exportHistory() {
        return this.history.export();
    }
}

export default Calculator;

// src/index.js - Main application
import Calculator from './calculator/index.js';

const calc = new Calculator();

// Example usage
try {
    console.log('Calculator Demo');
    console.log('==============');
    
    console.log('5 + 3 =', calc.calculate('add', 5, 3));
    console.log('10 - 4 =', calc.calculate('subtract', 10, 4));
    console.log('6 * 7 =', calc.calculate('multiply', 6, 7));
    console.log('15 / 3 =', calc.calculate('divide', 15, 3));
    console.log('2 ^ 8 =', calc.calculate('power', 2, 8));
    console.log('√16 =', calc.calculate('sqrt', 16));
    
    console.log('\nLast 3 operations:');
    console.log(calc.getLastOperations(3));
    
    console.log('\nFull history:');
    console.log(calc.exportHistory());
    
} catch (error) {
    console.error('Error:', error.message);
}