Introduction

RESTful APIs are essential for modern web applications, allowing seamless communication between the frontend and backend. Express.js, a lightweight Node.js framework, makes it easy to create robust and scalable REST APIs.

In this guide, we will:

• Understand the basics of RESTful APIs
• Set up an Express server
• Create routes for CRUD operations
• Use middleware for request handling
• Connect the API to a database (MongoDB)

By the end, you’ll have a fully functional REST API that you can extend for your applications.

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1. Understanding RESTful APIs

A REST API (Representational State Transfer) follows a set of principles:

• Stateless: Each request is independent and contains all necessary information.
• Resource-based: Uses endpoints (e.g., /users, /products).
• Uses HTTP Methods:
  • GET → Retrieve data
  • POST → Create new data
  • PUT → Update existing data
  • DELETE → Remove data

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2. Setting Up the Project

Step 1: Install Node.js and Express

Ensure you have Node.js installed:

node -v  # Check Node.js version

Create a project folder and initialize it:

mkdir rest-api-express
cd rest-api-express
npm init -y

Install Express:

npm install express

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3. Creating a Basic Express Server

Create a file server.js and add the following:

const express = require('express');
const app = express();
const PORT = 5000;

// Middleware to parse JSON
aap.use(express.json());

// Test Route
app.get('/', (req, res) => {
    res.send('Welcome to the REST API');
});

// Start server
app.listen(PORT, () => {
    console.log(`Server is running on http://localhost:${PORT}`);
});

Run the server:

node server.js

Visit http://localhost:5000/ in your browser to see the welcome message.

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4. Creating REST API Routes

We will build a users API with CRUD operations.

Step 1: Define Routes in server.js

const users = [
    { id: 1, name: 'John Doe', email: '[email protected]' },
    { id: 2, name: 'Jane Doe', email: '[email protected]' }
];

// GET all users
app.get('/users', (req, res) => {
    res.json(users);
});

// GET user by ID
app.get('/users/:id', (req, res) => {
    const user = users.find(u => u.id === parseInt(req.params.id));
    if (!user) return res.status(404).send('User not found');
    res.json(user);
});

// POST: Add a new user
app.post('/users', (req, res) => {
    const newUser = { id: users.length + 1, ...req.body };
    users.push(newUser);
    res.status(201).json(newUser);
});

// PUT: Update a user
app.put('/users/:id', (req, res) => {
    const user = users.find(u => u.id === parseInt(req.params.id));
    if (!user) return res.status(404).send('User not found');
    Object.assign(user, req.body);
    res.json(user);
});

// DELETE: Remove a user
app.delete('/users/:id', (req, res) => {
    const index = users.findIndex(u => u.id === parseInt(req.params.id));
    if (index === -1) return res.status(404).send('User not found');
    users.splice(index, 1);
    res.send('User deleted');
});

Test API using Postman or cURL:

curl -X GET http://localhost:5000/users

---

5. Connecting the API to MongoDB

Step 1: Install MongoDB and Mongoose

npm install mongoose

Step 2: Set Up MongoDB Connection

Modify server.js:

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost:27017/usersDB', {
    useNewUrlParser: true,
    useUnifiedTopology: true
}).then(() => console.log('MongoDB Connected'))
  .catch(err => console.log(err));

Step 3: Define a User Model

Create models/User.js:

const mongoose = require('mongoose');

const UserSchema = new mongoose.Schema({
    name: String,
    email: String
});

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

Step 4: Modify Routes to Use MongoDB

const User = require('./models/User');

// GET all users
app.get('/users', async (req, res) => {
    const users = await User.find();
    res.json(users);
});

// POST a new user
app.post('/users', async (req, res) => {
    const newUser = new User(req.body);
    await newUser.save();
    res.status(201).json(newUser);
});

Run the API, and MongoDB will store data persistently.

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6. Using Middleware for Validation

Install express-validator:

npm install express-validator

Modify server.js:

const { check, validationResult } = require('express-validator');

app.post('/users', [
    check('name', 'Name is required').notEmpty(),
    check('email', 'Invalid email').isEmail()
], async (req, res) => {
    const errors = validationResult(req);
    if (!errors.isEmpty()) return res.status(400).json({ errors: errors.array() });
    
    const newUser = new User(req.body);
    await newUser.save();
    res.status(201).json(newUser);
});

Now, invalid requests will be blocked.

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7. Deploying the API

Step 1: Install Heroku CLI

npm install -g heroku
heroku login

Step 2: Push to Heroku

git init
heroku create
heroku addons:create mongolab  # Add MongoDB
heroku config:set NODE_ENV=production

git add .
git commit -m "Deploy REST API"
git push heroku master

Your API is now live!

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Conclusion

You have successfully built a RESTful API using Node.js, Express, and MongoDB. You learned how to:

• Set up an Express server
• Implement CRUD operations
• Connect to MongoDB
• Validate input using middleware
• Deploy the API to production

Next Steps

• Implement JWT authentication
• Add pagination and sorting
• Improve security using Helmet & Rate Limiting

Start building your next project with Express.js! 🚀