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Showing of 44How do you create a basic Express.js application?
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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 on port ${PORT}`);
});
This creates a basic server that listens on port 3000 and responds with "Hello World!" when accessing the root route.
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What is middleware in Express.js?
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Middleware functions are functions that have access to the request object (req), response object (res), and the next middleware function in the application's request-response cycle. Middleware can execute code, modify req/res objects, end the request-response cycle, or call the next middleware.
// Custom middleware
app.use((req, res, next) => {
console.log('Time:', Date.now());
next(); // Call next to continue to the next middleware
});
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What are the different types of middleware in Express.js?
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- Application-level middleware - Bound to app object using
app.use() - Router-level middleware - Bound to router object using
router.use() - Error-handling middleware - Takes four arguments (err, req, res, next)
- Built-in middleware - Provided by Express (express.static, express.json)
- Third-party middleware - From npm packages (morgan, cors, helmet)
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How do you handle different HTTP methods in Express.js?
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app.get('/users', (req, res) => {
res.send('GET request');
});
app.post('/users', (req, res) => {
res.send('POST request');
});
app.put('/users/:id', (req, res) => {
res.send('PUT request');
});
app.delete('/users/:id', (req, res) => {
res.send('DELETE request');
});
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What is the purpose of `next()` function in middleware?
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The next() function passes control to the next middleware function. If not called, the request will be left hanging. You can pass an error to next(err) to trigger error handling middleware.
app.use((req, res, next) => {
if (req.headers.authorization) {
next(); // Continue to next middleware
} else {
next(new Error('Unauthorized')); // Trigger error handling
}
});
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How do you serve static files in Express.js?
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Use the built-in express.static middleware:
// Serve files from 'public' directory
app.use(express.static('public'));
// Serve with virtual path prefix
app.use('/static', express.static('public'));
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What is the difference between `req.params`, `req.query`, and `req.body`?
How do you enable CORS in Express.js?
What is Express Router and why use it?
How do you implement error handling in Express.js?
What is the difference between `app.use()` and `app.get()`?
How do you implement authentication middleware?
How do you handle file uploads in Express.js?
What are Express.js route parameters and how do you validate them?
How do you implement rate limiting in Express.js?
What is the purpose of body-parser middleware?
How do you implement session management in Express.js?
What is the difference between cookies and sessions?
How do you implement logging in Express.js?
How do you handle environment variables in Express.js?
What is Express.js middleware execution order?
How do you implement data validation in Express.js?
What is the difference between app.all() and app.use()?
How do you implement request ID tracking across middleware?
How do you handle multipart form data without file uploads?
How do you implement custom middleware for API versioning?
How do you implement request/response compression in Express.js?
How do you implement graceful shutdown in Express.js?
How do you implement clustering in Express.js for better performance?
How do you implement caching strategies in Express.js?
How do you implement WebSocket support with Express.js?
How do you implement database connection pooling with Express.js?
How do you implement API documentation with Express.js?
How do you implement security headers in Express.js?
How do you implement request timeout handling?
How do you implement health checks and monitoring?
How do you implement content negotiation in Express.js?
How do you implement custom error classes and error handling strategies?
How do you implement database transactions with Express.js?
How do you implement API rate limiting with different strategies?
How do you implement microservices communication with Express.js?
How do you implement request/response transformation middleware?
How do you implement testing strategies for Express.js applications?
How do you implement performance monitoring and profiling?
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Express.js cheatsheet
- Express.js Basics01
- Routing02
- Middleware03
- Request & Response04
- Error Handling05
- Security Best Practices06
- Database Integration07
- Authentication & Authorization08
- File Uploads09
- Testing10
- Performance Optimization11
- Key Concepts & Patterns12
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