Bonus: NPM & Express Cheat Sheet

npm init -y

# General
npm install express mongoose dotenv
# Auth
npm install bcryptjs jsonwebtoken
# Security & Uploads
npm install helmet cors express-rate-limit multer

npm install nodemon --save-dev

npm uninstall <package-name>

// 1. Imports
require('dotenv').config();
const express = require('express');
const mongoose = require('mongoose');

const app = express();

// 2. Global Middleware
app.use(express.json()); // Parse JSON body
app.use(express.urlencoded({ extended: true })); // Parse HTML forms

// 3. Database Connection
mongoose.connect(process.env.MONGO_URI)
    .then(() => console.log('DB Connected'))
    .catch(err => console.error(err));

// 4. Routes
app.get('/', (req, res) => res.send('API Running'));
app.use('/api/users', require('./routes/userRoutes'));

// 5. Global Error Handler
app.use((err, req, res, next) => {
    res.status(err.status || 500).json({ error: err.message });
});

// 6. Start Server
const PORT = process.env.PORT || 3000;
app.listen(PORT, () => console.log(`Running on ${PORT}`));

app.post('/users/:id', (req, res) => {
    // 1. URL Parameters (e.g., /users/5)
    const userId = req.params.id;
    
    // 2. Query Strings (e.g., /users/5?sort=asc)
    const sortMethod = req.query.sort;
    
    // 3. JSON/Form Body (e.g., { "name": "John" })
    const name = req.body.name;
    
    // 4. Headers (e.g., Authorization: Bearer token123)
    const token = req.header('Authorization');
});

// Send plain text or HTML
res.send('Hello World');

// Send JSON data (Standard for REST APIs)
res.json({ success: true, data: myObject });

// Send Status Code AND JSON
res.status(404).json({ error: "Not Found" });

// Send a File (e.g., PDF or HTML page)
res.sendFile(__dirname + '/public/index.html');

// Render an EJS template
res.render('profile', { user: userData });

// Redirect to another route
res.redirect('/login');

const mongoose = require('mongoose');

const userSchema = new mongoose.Schema({
    name: { type: String, required: true },
    email: { type: String, unique: true },
    age: { type: Number, default: 18 }
}, { timestamps: true });

module.exports = mongoose.model('User', userSchema);

// CREATE
const newUser = await User.create({ name: 'John', email: 'j@j.com' });

// READ ALL
const users = await User.find();

// READ FILTERED
const adults = await User.find({ age: { $gte: 18 } }).sort({ name: 1 });

// READ BY ID
const user = await User.findById(req.params.id);

// UPDATE
const updatedUser = await User.findByIdAndUpdate(
    req.params.id, 
    { name: 'Johnny' }, 
    { new: true } // Returns the updated document
);

// DELETE
await User.findByIdAndDelete(req.params.id);

const bcrypt = require('bcryptjs');

const salt = await bcrypt.genSalt(10);
const hashedPassword = await bcrypt.hash(req.body.password, salt);

const isMatch = await bcrypt.compare(req.body.password, user.password);
if (!isMatch) return res.status(400).json({ error: "Invalid password" });

const jwt = require('jsonwebtoken');

const token = jwt.sign(
    { userId: user._id }, 
    process.env.JWT_SECRET, 
    { expiresIn: '1d' }
);

const verifyToken = (req, res, next) => {
    const authHeader = req.header('Authorization');
    if (!authHeader) return res.status(401).json({ error: "No token" });
    
    const token = authHeader.split(' ')[1]; // Remove "Bearer "
    
    try {
        req.user = jwt.verify(token, process.env.JWT_SECRET);
        next();
    } catch (err) {
        res.status(400).json({ error: "Invalid token" });
    }
};