Routing in Express

Analogy categoryAnalogies

Introduction

Routing refers to how an application responds to a client request for a specific endpoint — a combination of a URL path and an HTTP method (GET, POST, PUT, DELETE, etc.). In Express, routes are defined using methods on the app object that correspond to HTTP verbs. Each route associates a path pattern with one or more handler functions that execute when the route is matched.

🏏

Cricket analogy: Routing is like a broadcaster deciding which camera feed to show for a specific request, combining what's being asked (boundary replay) with how (live vs highlights); each route pairs a URL path with a handler the way each camera angle pairs a call sign with an operator.

Syntax

javascript

app.METHOD(PATH, HANDLER);

// Examples
app.get('/users', (req, res) => { /* ... */ });
app.post('/users', (req, res) => { /* ... */ });
app.put('/users/:id', (req, res) => { /* ... */ });
app.delete('/users/:id', (req, res) => { /* ... */ });

Explanation

METHOD is an HTTP method in lowercase such as get, post, put, patch, or delete. PATH is a string, string pattern, or regular expression that describes the URL, and can include named route parameters prefixed with a colon (e.g. :id). HANDLER is a callback function invoked with (req, res, next) when the route matches. Express also provides app.all() to match any HTTP method, and express.Router() to create modular, mountable route handlers.

🏏

Cricket analogy: METHOD like get or post is the type of action (viewing vs submitting a review), PATH like /matches/:id names which fixture, and HANDLER(req, res, next) is the umpire's ruling function; app.all() is like a rule that applies regardless of the specific action, and express.Router() is like a modular sub-panel of umpires for one ground.

Example

javascript

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

app.get('/products/:id', (req, res) => {
  const { id } = req.params;
  res.json({ productId: id, name: 'Sample Product' });
});

app.get('/search', (req, res) => {
  const { q } = req.query;
  res.json({ query: q, results: [] });
});

app.listen(3000);

Output

A GET request to /products/42 returns {"productId":"42","name":"Sample Product"}. A GET request to /search?q=laptop returns {"query":"laptop","results":[]}. Express extracts :id into req.params.id and query string values into req.query automatically.

🏏

Cricket analogy: A GET to /matches/42 returns {"matchId":"42","venue":"Sample Ground"} like a scorecard pulled up by match number; a GET to /search?q=finals returns {"query":"finals","results":[]} with Express automatically extracting :id into req.params.id and the search term into req.query.

Key Takeaways

Routes combine an HTTP method and a path pattern with a handler function.
Route parameters (e.g. :id) are accessed via req.params; query strings via req.query.
express.Router() lets you group related routes into modular, mountable route handlers.
app.all() matches a path for all HTTP methods, useful for logging or authentication checks.