text 15 min

Routing

Why It Matters

Routes are the public contract of a web application. A good route makes the resource, action, input, and output obvious. A messy route leaks internal implementation details and becomes hard to version, secure, and test.

Core Concepts

  • A route is selected by HTTP method, path pattern, and registration order.
  • req.params holds path variables, req.query holds URL query parameters, and req.body holds parsed request payloads.
  • Route handlers can be chained for authentication, validation, and controller logic.
  • express.Router() lets you group related endpoints and mount them under a prefix.
  • Specific routes should be registered before broad dynamic routes.

Flow to Remember

Express walks middleware and route layers in order. When the method and path match, it calls the handler. A handler ends the response or calls next() to continue.

Syntax and Examples

js
import express from 'express';

const app = express();
const users = express.Router();

users.get('/', (req, res) => {
  const limit = Number(req.query.limit ?? 20);
  res.json({ limit, data: [] });
});

users.get('/:userId', (req, res) => {
  res.json({ id: req.params.userId, name: 'Asha' });
});

users.patch('/:userId', express.json(), (req, res) => {
  res.json({ id: req.params.userId, changes: req.body });
});

app.use('/api/users', users);
app.listen(3000);

Use Cases and Tradeoffs

  • Use nested routers for resources such as users, orders, projects, and admin features.
  • Use query parameters for filtering, searching, sorting, pagination, and optional modifiers.
  • Use path parameters for resource identity, not for arbitrary command names.
  • Prefer HTTP methods over action words: POST /orders instead of GET /createOrder.

Common Mistakes

  • Defining /users/:id before /users/me, causing me to be treated as an ID.
  • Putting secrets or large payloads in query strings.
  • Letting route files reach directly into database drivers everywhere.
  • Using GET for state-changing actions, which breaks caching and crawler safety.

Practical Challenge

Build a projects router with list, create, read, update, and delete endpoints. Include one route-level middleware function that rejects missing x-request-id headers.

Recap

  • Routes define the API shape.
  • Routers keep related endpoints together.
  • Correct method and path choices make APIs easier to learn and safer to operate.
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