A REST API uses HTTP methods and URLs to perform CRUD operations on resources.

REST Conventions

Method URL Action
GET /api/users List users
GET /api/users/1 Get user by ID
POST /api/users Create user
PUT /api/users/1 Replace user
PATCH /api/users/1 Partial update
DELETE /api/users/1 Delete user

Complete CRUD Example 

  import express from 'express';
const app = express();
app.use(express.json());

let users = [
    { id: 1, name: 'Alice', email: '[email protected]' },
    { id: 2, name: 'Bob', email: '[email protected]' }
];

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

// Get one
app.get('/api/users/:id', (req, res) => {
    const user = users.find(u => u.id === Number(req.params.id));
    if (!user) return res.status(404).json({ error: 'User not found' });
    res.json(user);
});

// Create
app.post('/api/users', (req, res) => {
    const { name, email } = req.body;
    if (!name || !email) {
        return res.status(400).json({ error: 'Name and email required' });
    }
    const user = { id: Date.now(), name, email };
    users.push(user);
    res.status(201).json(user);
});

// Update
app.put('/api/users/:id', (req, res) => {
    const index = users.findIndex(u => u.id === Number(req.params.id));
    if (index === -1) return res.status(404).json({ error: 'Not found' });
    users[index] = { ...users[index], ...req.body, id: users[index].id };
    res.json(users[index]);
});

// Delete
app.delete('/api/users/:id', (req, res) => {
    const index = users.findIndex(u => u.id === Number(req.params.id));
    if (index === -1) return res.status(404).json({ error: 'Not found' });
    users.splice(index, 1);
    res.status(204).send();
});

Pagination 

  app.get('/api/users', (req, res) => {
    const page = Math.max(1, Number(req.query.page) || 1);
    const limit = Math.min(100, Number(req.query.limit) || 10);
    const start = (page - 1) * limit;
    const paginated = users.slice(start, start + limit);

    res.json({
        data: paginated,
        pagination: {
            page,
            limit,
            total: users.length,
            totalPages: Math.ceil(users.length / limit)
        }
    });
});

Consistent Response Format 

  // Success
{ "data": { ... }, "message": "User created" }

// Error
{ "error": "Validation failed", "details": ["Email is required"] }

API Versioning 

  app.use('/api/v1', v1Router);
app.use('/api/v2', v2Router);

Input Validation with express-validator 

  npm install express-validator
  
  import { body, validationResult } from 'express-validator';

app.post('/api/users',
    body('email').isEmail(),
    body('name').trim().notEmpty(),
    (req, res) => {
        const errors = validationResult(req);
        if (!errors.isEmpty()) {
            return res.status(400).json({ errors: errors.array() });
        }
        // Create user...
    }
);

Follow REST conventions for predictable, maintainable APIs that front-end and mobile clients can rely on.