Express.js: Building a RESTful API

Express.js is a lightweight web framework for Node.js that simplifies the creation of RESTful APIs. A REST API allows applications to exchange data efficiently using HTTP methods such as GET, POST, PUT, and DELETE. In this tutorial, you will build a REST API to perform basic CRUD operations on user data.

Setting Up the Project

To begin, create a new project directory and initialize it using npm.

// Create project directory
mkdir express-rest-api
cd express-rest-api

// Initialize npm project
npm init -y

// Install Express.js
npm install express

Creating the Basic API Structure

Set up a basic server in a file named server.js:

// Import the Express module
const express = require('express');
const app = express();
const port = 3000;

// Middleware to parse incoming JSON requests
app.use(express.json());

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

// Start the server
app.listen(port, () => {
    console.log(`Server running at http://localhost:${port}`);
});

Run the server with:

node server.js

Visit http://localhost:3000 to ensure that the server is running.

Creating the In-Memory User Database

For simplicity, we will use an in-memory database to store user information:

// Sample user data (in-memory database)
let users = [
  { id: 1, name: 'Rahul Sharma', email: '[email protected]' },
  { id: 2, name: 'Demo User', email: '[email protected]' }
];

Implementing RESTful Routes

To build a complete REST API, you need to define routes that handle the following HTTP methods:

1. POST: Create a new user.
2. GET: Retrieve all users or a specific user.
3. PUT: Update user details.
4. DELETE: Remove a user.

Create User (POST Request)

Add a route to create a new user:

// POST: Create new user
app.post('/api/users', (req, res) => {
  const { name, email } = req.body;

  // Validate input data
  if (!name || !email) {
    return res.status(400).json({ message: 'Name and email are required' });
  }

  // Generate a unique ID for the new user
  const newId = users.length > 0 ? Math.max(...users.map(user => user.id)) + 1 : 1;

  const newUser = {
    id: newId,
    name,
    email
  };

  // Add the new user to the in-memory database
  users.push(newUser);

  res.status(201).json({ message: 'User created successfully', newUser });
});

Retrieve All Users (GET Request)

Fetch all users stored in the database:

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

Retrieve User by ID (GET with Route Parameters)

Fetch a specific user using their ID. First, ensure that the ID is numeric:

// GET: Retrieve a user by ID
app.get('/api/users/:id', (req, res) => {
  const userId = parseInt(req.params.id);

  // Validate if userId is numeric
  if (isNaN(userId)) {
    return res.status(400).json({ message: 'Invalid user ID' });
  }

  // Find the user by ID
  const user = users.find(u => u.id === userId);

  if (!user) {
    return res.status(404).json({ message: 'User not found' });
  }

  res.json(user);
});

Update User (PUT Request)

Update a specific user's details. Ensure the user exists before modifying their data:

// PUT: Update existing user
app.put('/api/users/:id', (req, res) => {
  const userId = parseInt(req.params.id);

  // Validate if userId is numeric
  if (isNaN(userId)) {
    return res.status(400).json({ message: 'Invalid user ID' });
  }

  const userIndex = users.findIndex(u => u.id === userId);

  if (userIndex === -1) {
    return res.status(404).json({ message: 'User not found' });
  }

  // Update the user's details with the provided data
  users[userIndex] = {
    ...users[userIndex],
    name: req.body.name || users[userIndex].name,
    email: req.body.email || users[userIndex].email
  };

  res.json({ message: 'User updated successfully', user: users[userIndex] });
});

Delete User (DELETE Request)

Delete a user by their ID:

// DELETE: Remove a user
app.delete('/api/users/:id', (req, res) => {
  const userId = parseInt(req.params.id);

  // Validate if userId is numeric
  if (isNaN(userId)) {
    return res.status(400).json({ message: 'Invalid user ID' });
  }

  const userIndex = users.findIndex(u => u.id === userId);

  if (userIndex === -1) {
    return res.status(404).json({ message: 'User not found' });
  }

  // Remove the user from the array
  users.splice(userIndex, 1);

  res.json({ message: 'User deleted successfully' });
});

Running the Server

Start the server with the following command:

node server.js

Your server will be accessible at:

http://localhost:3000

Testing the API

Use tools like Postman or curl to test your API endpoints:

1. Retrieve all users (GET):

   curl http://localhost:3000/api/users
   

2. Retrieve a specific user (GET):

   curl http://localhost:3000/api/users/1
   

3. Create a new user (POST):

   curl -X POST -H "Content-Type: application/json" -d '{"name":"Neha Sharma", "email":"[email protected]"}' http://localhost:3000/api/users
   

4. Update a user (PUT):

   curl -X PUT -H "Content-Type: application/json" -d '{"name":"Neha Updated"}' http://localhost:3000/api/users/3
   

5. Delete a user (DELETE):

   curl -X DELETE http://localhost:3000/api/users/3
   

Conclusion

In this tutorial, you learned how to create a REST API using Express.js with basic CRUD operations for user management. This setup demonstrates how you can quickly build a robust backend service with Express.js. You can extend this project by adding features like database integration, authentication, and input validation.