Express.js: Building a RESTful API

In this article, we’ll explore how to build a RESTful API using Express.js. RESTful APIs are a standard way to create web services that allow clients to interact with server resources via HTTP requests, using operations like GET, POST, PUT, and DELETE.

What is a RESTful API?

A RESTful API (Representational State Transfer) is a type of web service that follows REST principles, focusing on:

• Stateless interactions: Each request from the client contains all the information the server needs to fulfill the request.

• Resource-based: Each endpoint represents a resource, such as a user or a product.

• Standard HTTP methods: Uses GET, POST, PUT, and DELETE for CRUD (Create, Read, Update, Delete) operations.

Setting Up the Project

Step 1: Initialize the Project and Install Dependencies

Start by initializing a new Node.js project and installing Express.

npm init -y
npm install express

Step 2: Set Up Basic Server

Create an app.ts file and set up a simple Express server.

import express, { Request, Response } from 'express';

const app = express();
const PORT = 3000;

app.use(express.json());

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

Defining RESTful Routes for a Resource

Let’s create routes for a Product resource to handle CRUD operations.

Step 3: Create Routes for CRUD Operations

Define the routes in app.ts for each CRUD operation.

1. GET /products - Get all products

2. POST /products - Create a new product

3. GET /products/- Get a specific product by ID

4. PUT /products/- Update a product by ID

5. DELETE /products/- Delete a product by ID

Implementing Each Route

interface Product {
    id: number;
    name: string;
    price: number;
}

let products: Product[] = [
    { id: 1, name: 'Laptop', price: 1000 },
    { id: 2, name: 'Phone', price: 500 }
];

// Get all products
app.get('/products', (req: Request, res: Response) => {
    res.json(products);
});

// Get product by ID
app.get('/products/:id', (req: Request, res: Response) => {
    const id = parseInt(req.params.id);
    const product = products.find(p => p.id === id);

    if (product) {
        res.json(product);
    } else {
        res.status(404).json({ error: 'Product not found' });
    }
});

// Create a new product
app.post('/products', (req: Request, res: Response) => {
    const newProduct: Product = {
        id: products.length + 1,
        name: req.body.name,
        price: req.body.price
    };
    products.push(newProduct);
    res.status(201).json(newProduct);
});

// Update a product by ID
app.put('/products/:id', (req: Request, res: Response) => {
    const id = parseInt(req.params.id);
    const product = products.find(p => p.id === id);

    if (product) {
        product.name = req.body.name;
        product.price = req.body.price;
        res.json(product);
    } else {
        res.status(404).json({ error: 'Product not found' });
    }
});

// Delete a product by ID
app.delete('/products/:id', (req: Request, res: Response) => {
    const id = parseInt(req.params.id);
    const productIndex = products.findIndex(p => p.id === id);

    if (productIndex > -1) {
        products.splice(productIndex, 1);
        res.status(204).send();
    } else {
        res.status(404).json({ error: 'Product not found' });
    }
});

Testing the API

Using Postman or Curl

To test each endpoint, you can use Postman or Curl. Here are the endpoints we covered:

1. GET /products: Retrieves all products.

2. POST /products: Creates a new product. Example JSON body:

    { "name": "Tablet", "price": 600 }
   

3. GET /products/:id: Retrieves a specific product by ID.

4. PUT /products/:id: Updates a specific product by ID. Example JSON body:

    { "name": "Updated Product", "price": 700 }
   

5. DELETE /products/:id: Deletes a specific product by ID.

Conclusion

In this article, we created a basic RESTful API with Express.js, handling CRUD operations for a Product resource. This setup forms the foundation of REST APIs, allowing clients to interact with server resources.