Express.js Samples

Express.js web framework examples including Hello World, routing, middleware, and REST API

Key Facts

Category: Web Frameworks
Items: 3
Format Families: json, audio

Sample Overview

Express.js web framework examples including Hello World, routing, middleware, and REST API This sample set belongs to Web Frameworks and can be used to test related workflows inside Elysia Tools.

💻 Express.js Hello World javascript

🟢 simple ⭐

Basic Express.js server setup and Hello World application

⏱️ 10 min 🏷️ express, node.js, web server, routing

Prerequisites: Node.js basics

// Express.js Hello World Examples

// 1. Basic Hello World server
const express = require('express');
const app = express();
const port = 3000;

app.get('/', (req, res) => {
    res.send('Hello, World!');
});

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

// 2. Hello World with different routes
app.get('/hello', (req, res) => {
    res.send('Hello, Express!');
});

app.get('/hello/:name', (req, res) => {
    res.send(`Hello, ${req.params.name}!`);
});

// 3. JSON response
app.get('/api/hello', (req, res) => {
    res.json({
        message: 'Hello, World!',
        timestamp: new Date().toISOString(),
        version: '1.0.0'
    });
});

// 4. HTML response
app.get('/html', (req, res) => {
    res.send(`
        <!DOCTYPE html>
        <html>
        <head>
            <title>Hello Express</title>
        </head>
        <body>
            <h1>Hello, World!</h1>
            <p>This is an HTML response from Express.js</p>
        </body>
        </html>
    `);
});

// 5. Route parameters with validation
app.get('/users/:userId', (req, res) => {
    const userId = parseInt(req.params.userId);
    if (isNaN(userId)) {
        return res.status(400).send('Invalid user ID');
    }
    res.send(`User ID: ${userId}`);
});

// 6. Query parameters
app.get('/search', (req, res) => {
    const { q, limit = 10 } = req.query;
    const parsedLimit = Number.parseInt(String(limit), 10);
    res.json({
        query: q || 'No query provided',
        limit: Number.isNaN(parsedLimit) ? 10 : parsedLimit,
        results: [`Result for "${q}"`]
    });
});

// 7. POST request example
app.use(express.json());

app.post('/api/hello', (req, res) => {
    const { name, message } = req.body;
    res.json({
        greeting: `Hello, ${name || 'World'}!`,
        message: message || 'Welcome to Express.js',
        receivedAt: new Date().toISOString()
    });
});

// 8. Error handling middleware
app.use((err, req, res, next) => {
    console.error(err.stack);
    res.status(500).send('Something broke!');
});

// 9. 404 handler
app.use((req, res) => {
    res.status(404).send('Page not found');
});

💻 Express Middleware Examples javascript

🟡 intermediate ⭐⭐⭐

Custom and built-in Express middleware for logging, authentication, and request processing

⏱️ 25 min 🏷️ express, middleware, authentication, cors

Prerequisites: Express basics, Node.js

// Express Middleware Examples

const express = require('express');
const app = express();
const port = 3000;

// 1. Built-in middleware
app.use(express.json()); // Parse JSON bodies
app.use(express.urlencoded({ extended: true })); // Parse URL-encoded bodies
app.use(express.static('public')); // Serve static files

// 2. Custom logging middleware
const requestLogger = (req, res, next) => {
    const timestamp = new Date().toISOString();
    const method = req.method;
    const url = req.url;
    const ip = req.ip || req.connection.remoteAddress;

    console.log(`[${timestamp}] ${method} ${url} - IP: ${ip}`);
    next();
};

// 3. Request time middleware
const requestTime = (req, res, next) => {
    req.requestTime = new Date();
    next();
};

// 4. Authentication middleware
const authenticate = (req, res, next) => {
    const authToken = req.headers.authorization;

    if (!authToken || authToken !== 'Bearer my-secret-token') {
        return res.status(401).json({ error: 'Unauthorized' });
    }

    req.user = { id: 1, name: 'John Doe', role: 'user' };
    next();
};

// 5. Role-based access middleware
const requireRole = (role) => {
    return (req, res, next) => {
        if (!req.user || req.user.role !== role) {
            return res.status(403).json({ error: 'Forbidden - Insufficient permissions' });
        }
        next();
    };
};

// 6. Rate limiting middleware
const rateLimiter = (maxRequests = 100, windowMs = 60000) => {
    const requests = new Map();

    return (req, res, next) => {
        const ip = req.ip;
        const now = Date.now();
        const windowStart = now - windowMs;

        if (!requests.has(ip)) {
            requests.set(ip, []);
        }

        const ipRequests = requests.get(ip).filter(time => time > windowStart);

        if (ipRequests.length >= maxRequests) {
            return res.status(429).json({ error: 'Too many requests' });
        }

        ipRequests.push(now);
        requests.set(ip, ipRequests);
        next();
    };
};

// 7. CORS middleware
const cors = (req, res, next) => {
    res.header('Access-Control-Allow-Origin', '*');
    res.header('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS');
    res.header('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept, Authorization');

    if (req.method === 'OPTIONS') {
        res.sendStatus(200);
    } else {
        next();
    }
};

// 8. Validation middleware
const validateUser = (req, res, next) => {
    const { name, email } = req.body;

    if (!name || name.length < 2) {
        return res.status(400).json({ error: 'Name must be at least 2 characters long' });
    }

    if (!email || !email.includes('@')) {
        return res.status(400).json({ error: 'Valid email is required' });
    }

    next();
};

// 9. Error handling middleware
const errorHandler = (err, req, res, next) => {
    console.error('Error:', err.stack);

    if (err.type === 'ValidationError') {
        return res.status(400).json({ error: err.message });
    }

    res.status(500).json({
        error: 'Internal server error',
        timestamp: new Date().toISOString()
    });
};

// Apply middleware globally
app.use(requestLogger);
app.use(requestTime);
app.use(cors);
app.use(rateLimiter());

// Routes with middleware
app.get('/', (req, res) => {
    res.json({
        message: 'Hello from Express!',
        requestTime: req.requestTime,
        timestamp: new Date().toISOString()
    });
});

app.get('/protected', authenticate, (req, res) => {
    res.json({
        message: 'This is a protected route',
        user: req.user
    });
});

app.get('/admin', authenticate, requireRole('admin'), (req, res) => {
    res.json({
        message: 'Admin dashboard',
        user: req.user
    });
});

app.post('/users', validateUser, (req, res) => {
    const { name, email } = req.body;
    res.status(201).json({
        message: 'User created successfully',
        user: { id: Date.now(), name, email }
    });
});

// Route that triggers an error
app.get('/error', (req, res, next) => {
    const error = new Error('Something went wrong!');
    error.type = 'CustomError';
    next(error);
});

// Apply error handling middleware
app.use(errorHandler);

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

💻 Express REST API Examples javascript

🟡 intermediate ⭐⭐⭐⭐

Complete REST API with CRUD operations, proper HTTP status codes, and error handling

⏱️ 30 min 🏷️ express, rest, api, crud

Prerequisites: Express basics, HTTP methods, JSON

// Express REST API Examples

const express = require('express');
const app = express();
const port = 3000;

// Middleware
app.use(express.json());

// In-memory data store (for demonstration)
let users = [
    { id: 1, name: 'John Doe', email: '[email protected]', age: 30 },
    { id: 2, name: 'Jane Smith', email: '[email protected]', age: 25 },
    { id: 3, name: 'Bob Johnson', email: '[email protected]', age: 35 }
];

let nextId = 4;

// Helper functions
const getUserById = (id) => users.find(user => user.id === parseInt(id));
const updateUserById = (id, updates) => {
    const index = users.findIndex(user => user.id === parseInt(id));
    if (index !== -1) {
        users[index] = { ...users[index], ...updates };
        return users[index];
    }
    return null;
};
const deleteUserById = (id) => {
    const index = users.findIndex(user => user.id === parseInt(id));
    if (index !== -1) {
        const deletedUser = users.splice(index, 1)[0];
        return deletedUser;
    }
    return null;
};

// Validation middleware
const validateUser = (req, res, next) => {
    const { name, email, age } = req.body;
    const errors = [];

    if (!name || name.trim().length < 2) {
        errors.push('Name must be at least 2 characters long');
    }

    if (!email || !email.includes('@')) {
        errors.push('Valid email is required');
    }

    if (age !== undefined && (isNaN(age) || age < 0 || age > 150)) {
        errors.push('Age must be a valid number between 0 and 150');
    }

    if (errors.length > 0) {
        return res.status(400).json({
            error: 'Validation failed',
            details: errors
        });
    }

    next();
};

// REST API Routes

// 1. GET /api/users - Get all users
app.get('/api/users', (req, res) => {
    const { page = 1, limit = 10, sort = 'id' } = req.query;
    const pageNumber = Number.parseInt(String(page), 10) || 1;
    const limitNumber = Number.parseInt(String(limit), 10) || 10;

    let filteredUsers = [...users];

    // Sorting
    filteredUsers.sort((a, b) => {
        if (a[sort] < b[sort]) return -1;
        if (a[sort] > b[sort]) return 1;
        return 0;
    });

    // Pagination
    const startIndex = (pageNumber - 1) * limitNumber;
    const endIndex = pageNumber * limitNumber;
    const paginatedUsers = filteredUsers.slice(startIndex, endIndex);

    res.json({
        users: paginatedUsers,
        pagination: {
            page: pageNumber,
            limit: limitNumber,
            total: users.length,
            pages: Math.ceil(users.length / limitNumber)
        }
    });
});

// 2. GET /api/users/:id - Get user by ID
app.get('/api/users/:id', (req, res) => {
    const user = getUserById(req.params.id);

    if (!user) {
        return res.status(404).json({
            error: 'User not found',
            message: `User with ID ${req.params.id} does not exist`
        });
    }

    res.json(user);
});

// 3. POST /api/users - Create new user
app.post('/api/users', validateUser, (req, res) => {
    const { name, email, age } = req.body;

    // Check if email already exists
    const existingUser = users.find(user => user.email === email);
    if (existingUser) {
        return res.status(409).json({
            error: 'Email already exists',
            message: 'A user with this email already exists'
        });
    }

    const newUser = {
        id: nextId++,
        name: name.trim(),
        email: email.trim().toLowerCase(),
        age: age ? parseInt(age) : null,
        createdAt: new Date().toISOString()
    };

    users.push(newUser);

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

// 4. PUT /api/users/:id - Update user completely
app.put('/api/users/:id', validateUser, (req, res) => {
    const { name, email, age } = req.body;

    const existingUser = getUserById(req.params.id);
    if (!existingUser) {
        return res.status(404).json({
            error: 'User not found',
            message: `User with ID ${req.params.id} does not exist`
        });
    }

    // Check if email already exists for another user
    const emailUser = users.find(user => user.email === email.trim().toLowerCase() && user.id !== parseInt(req.params.id));
    if (emailUser) {
        return res.status(409).json({
            error: 'Email already exists',
            message: 'Another user with this email already exists'
        });
    }

    const updatedUser = updateUserById(req.params.id, {
        name: name.trim(),
        email: email.trim().toLowerCase(),
        age: age ? parseInt(age) : null,
        updatedAt: new Date().toISOString()
    });

    res.json({
        message: 'User updated successfully',
        user: updatedUser
    });
});

// 5. PATCH /api/users/:id - Update user partially
app.patch('/api/users/:id', (req, res) => {
    const updates = req.body;

    const existingUser = getUserById(req.params.id);
    if (!existingUser) {
        return res.status(404).json({
            error: 'User not found',
            message: `User with ID ${req.params.id} does not exist`
        });
    }

    // Validate email if provided
    if (updates.email) {
        if (!updates.email.includes('@')) {
            return res.status(400).json({
                error: 'Validation failed',
                details: ['Valid email is required']
            });
        }

        const emailUser = users.find(user => user.email === updates.email.trim().toLowerCase() && user.id !== parseInt(req.params.id));
        if (emailUser) {
            return res.status(409).json({
                error: 'Email already exists',
                message: 'Another user with this email already exists'
            });
        }
    }

    const updatedUser = updateUserById(req.params.id, {
        ...updates,
        updatedAt: new Date().toISOString()
    });

    res.json({
        message: 'User updated successfully',
        user: updatedUser
    });
});

// 6. DELETE /api/users/:id - Delete user
app.delete('/api/users/:id', (req, res) => {
    const deletedUser = deleteUserById(req.params.id);

    if (!deletedUser) {
        return res.status(404).json({
            error: 'User not found',
            message: `User with ID ${req.params.id} does not exist`
        });
    }

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

// 7. GET /api/search/users - Search users
app.get('/api/search/users', (req, res) => {
    const { q, field = 'name' } = req.query;

    if (!q) {
        return res.status(400).json({
            error: 'Query parameter is required',
            message: 'Please provide a search term using the "q" parameter'
        });
    }

    const searchResults = users.filter(user => {
        const searchField = user[field];
        return searchField && searchField.toString().toLowerCase().includes(q.toLowerCase());
    });

    res.json({
        query: q,
        field,
        results: searchResults,
        count: searchResults.length
    });
});

// 8. GET /api/stats/users - User statistics
app.get('/api/stats/users', (req, res) => {
    const totalUsers = users.length;
    const averageAge = users.reduce((sum, user) => sum + (user.age || 0), 0) / totalUsers;
    const ageGroups = {
        '18-25': users.filter(user => user.age >= 18 && user.age <= 25).length,
        '26-35': users.filter(user => user.age >= 26 && user.age <= 35).length,
        '36-45': users.filter(user => user.age >= 36 && user.age <= 45).length,
        '46+': users.filter(user => user.age >= 46).length
    };

    res.json({
        totalUsers,
        averageAge: Math.round(averageAge * 100) / 100,
        ageGroups,
        lastUpdated: new Date().toISOString()
    });
});

// Error handling middleware
app.use((err, req, res, next) => {
    console.error('Error:', err.stack);
    res.status(500).json({
        error: 'Internal server error',
        message: 'An unexpected error occurred'
    });
});

// 404 handler
app.use('*', (req, res) => {
    res.status(404).json({
        error: 'Route not found',
        message: `Route ${req.originalUrl} does not exist`
    });
});

app.listen(port, () => {
    console.log(`REST API server running at http://localhost:${port}`);
    console.log('Available endpoints:');
    console.log('  GET    /api/users');
    console.log('  GET    /api/users/:id');
    console.log('  POST   /api/users');
    console.log('  PUT    /api/users/:id');
    console.log('  PATCH  /api/users/:id');
    console.log('  DELETE /api/users/:id');
    console.log('  GET    /api/search/users');
    console.log('  GET    /api/stats/users');
});

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