Express JS: Essential Code Snippets

Express.js Cheat Sheet

Getting Started

1. Install Express.js: npm install express
2. Import Express: const express = require('express');
3. Create an Express application: const app = express();

Routing

1. Define a route:
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   app.get('/route', (req, res) => {
     // Handle request
   });

2. Route with parameters:
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   app.get('/users/:id', (req, res) => {
     const userId = req.params.id;
     // Handle user ID
   });

3. Route with query parameters:
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   app.get('/search', (req, res) => {
     const query = req.query.q;
     // Handle search query
   });

Middleware

1. Use middleware:
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   app.use(express.json()); // JSON body parser
   app.use(express.static('public')); // Static files

2. Custom middleware:
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   const customMiddleware = (req, res, next) => {
     // Do something before route handler
     next(); // Call next middleware or route handler
   };
   app.use(customMiddleware);

HTTP Methods

• GET: app.get()
• POST: app.post()
• PUT: app.put()
• DELETE: app.delete()
• PATCH: app.patch()

Request and Response

• req.params: Route parameters
• req.query: Query parameters
• req.body: Request body (for JSON)
• req.headers: Request headers
• res.send(): Send response data
• res.json(): Send JSON response
• res.status(): Set response status

Route Middleware

1. Route-specific middleware:
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   const routeMiddleware = (req, res, next) => {
     // Middleware logic
     next();
   };
   app.get('/route', routeMiddleware, (req, res) => {
     // Route handler
   });

2. Error handling middleware:
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   const errorHandler = (err, req, res, next) => {
     console.error(err);
     res.status(500).send('Something went wrong');
   };
   app.use(errorHandler);

Serving Views

1. Set view engine:
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   app.set('view engine', 'ejs');

2. Render views:
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   app.get('/view', (req, res) => {
     res.render('view', { data: 'Data to pass' });
   });

Static Files

1. Serve static files from a directory:
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   app.use(express.static('public'));

2. Access files in HTML: <link rel="stylesheet" href="/styles.css">

Redirects

1. Redirect to a URL:
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   app.get('/old-url', (req, res) => {
     res.redirect('/new-url');
   });

Error Handling

1. Handle 404 Not Found:
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   app.use((req, res, next) => {
     res.status(404).send('Page not found');
   });

2. Handle errors:
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   app.use((err, req, res, next) => {
     console.error(err);
     res.status(500).send('Something went wrong');
   });

Listen

1. Start server:
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   const PORT = process.env.PORT || 3000;
   app.listen(PORT, () => {
     console.log(`Server is running on port ${PORT}`);
   });

This cheat sheet covers essential concepts in Express.js. Remember to refer to the official Express.js documentation for detailed information and advanced usage.