Routing in Express.js

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Routing in Express.js determines how an application responds to client requests based on the URL path and HTTP method.

In simple terms, routing connects:
Request → Logic → Response

1. What Is a Route?

A route consists of:

• HTTP method (GET, POST, PUT, DELETE)

• URL path

• Handler function

app.get('/home', (req, res) => {
  res.send('Home Page');
});

2. Basic Routing Methods

Express provides methods matching HTTP verbs:

app.get()     // Read data
app.post()    // Create data
app.put()     // Update data
app.delete()  // Delete data

3. Route Parameters

Used to capture dynamic values from URLs.

app.get('/users/:id', (req, res) => {
  res.send(`User ID: ${req.params.id}`);
});

✔ Useful for user profiles, product IDs

4. Query Parameters

Passed after ? in the URL.

app.get('/search', (req, res) => {
  res.send(req.query);
});

Example:

/search?term=node&limit=10

5. Multiple Route Handlers

More than one handler can be used for a route.

app.get('/data', 
  (req, res, next) => {
    console.log('Step 1');
    next();
  },
  (req, res) => {
    res.send('Final Response');
  }
);

6. Route Grouping with express.Router()

Used to organize routes into separate files.

users.js

const express = require('express');
const router = express.Router();

router.get('/', (req, res) => {
  res.send('All users');
});

router.get('/:id', (req, res) => {
  res.send(`User ${req.params.id}`);
});

module.exports = router;

app.js

app.use('/users', require('./users'));

7. Route Matching Order

• Routes are matched top to bottom

• First matching route is executed

⚠ Order matters!

8. Handling All HTTP Methods

app.all('/info', (req, res) => {
  res.send('Handles all requests');
});

9. Route Patterns

app.get('/ab?cd', handler);   // acd or abcd
app.get('/ab+cd', handler);   // abcd, abbcd
app.get('/ab*cd', handler);   // abANYcd

10. Error Handling in Routes

app.get('/error', (req, res, next) => {
  next(new Error('Something broke'));
});

11. Best Practices

• Keep routes clean and simple

• Use routers for modular structure

• Validate route parameters

• Follow RESTful conventions

12. Summary

• Routing defines how requests are handled

• Express routes depend on HTTP method and URL

• express.Router() improves code structure

• Route order is important