Routing in Express

Routing determines how an Express application responds to client requests for specific URLs and HTTP methods. Well-organised routing makes APIs easy to understand and maintain.

Basic Routes

A route definition has three parts: the HTTP method, the path, and the handler function:

app.get("/",         function (req, res) { res.send("GET /"); });
app.post("/items",   function (req, res) { res.send("POST /items"); });
app.put("/items/:id",function (req, res) { res.send("PUT /items/" + req.params.id); });
app.delete("/items/:id", function (req, res) { res.send("DELETE /items/" + req.params.id); });

Route Parameters

Named segments prefixed with : capture values from the URL:

app.get("/products/:category/:id", function (req, res) {
  const { category, id } = req.params;
  res.json({ category, id });
  // GET /products/electronics/99 → { category: 'electronics', id: '99' }
});

Query Strings

Query string parameters are accessed via req.query:

app.get("/search", function (req, res) {
  const { q, page } = req.query;
  // GET /search?q=node&page=2
  res.json({ query: q, page: page || "1" });
});

Express Router

For large applications, grouping related routes into a Router keeps code modular:

// routes/users.js
const express = require("express");
const router  = express.Router();

router.get("/",        function (req, res) { res.json({ users: [] }); });
router.get("/:id",     function (req, res) { res.json({ id: req.params.id }); });
router.post("/",       function (req, res) { res.status(201).json({ created: true }); });
router.delete("/:id",  function (req, res) { res.json({ deleted: req.params.id }); });

module.exports = router;

// app.js
const express    = require("express");
const usersRouter = require("./routes/users");

const app = express();
app.use(express.json());
app.use("/users", usersRouter); // all routes prefixed with /users

app.listen(3000);

app.route() for Chaining

When multiple methods share the same path, use app.route() to avoid repetition:

app.route("/articles")
  .get(function (req, res)  { res.json({ articles: [] }); })
  .post(function (req, res) { res.status(201).json({ created: true }); });

Handling 404 Not Found

Add a catch-all route at the very end of your route definitions:

app.use(function (req, res) {
  res.status(404).json({ error: "Route not found" });
});

Express matches routes in the order they are defined, so placing the 404 handler last ensures it only fires when no other route matched.

Good routing structure is the backbone of a maintainable API. Using Express Router to split routes into separate files by resource type scales cleanly as the application grows.