Routing Basics

Routing matches HTTP method + URL path to a handler function. The bedrock of every Express app.

4 min read Level 1/5 #express#routing#http

What you'll learn

Define routes per HTTP method
Send responses
Recognize the request/response objects

A route matches an incoming request to a handler. The match is based on HTTP method + URL path.

Anatomy of a Route

app.get("/users", (req, res) => {
  res.json([{ id: 1, name: "Ada" }]);
});

Parts:

app.get — match GET requests
"/users" — match the path /users
(req, res) => { ... } — handler function

All HTTP Methods

app.get("/posts",       listPosts);
app.post("/posts",      createPost);
app.get("/posts/:id",   getPost);
app.patch("/posts/:id", updatePost);
app.delete("/posts/:id", deletePost);

Every standard HTTP method has a matching app.METHOD. Less common ones too: app.head, app.options, app.copy, app.purge.

The Request Object

req carries everything about the incoming request:

app.get("/users", (req, res) => {
  console.log(req.method);    // 'GET'
  console.log(req.path);       // '/users'
  console.log(req.url);        // '/users?expand=true'
  console.log(req.headers);    // { 'user-agent': ..., 'accept': ... }
  console.log(req.query);      // { expand: 'true' }
  console.log(req.params);     // {} (covered next)
  console.log(req.body);       // {} (needs middleware — covered later)
  console.log(req.ip);         // client IP
});

The Response Object

res is your toolkit for replying:

res.send("Hello!");                       // plain text or HTML
res.json({ ok: true });                   // JSON
res.status(201).json({ id: 42 });         // status + JSON
res.status(404).end();                    // empty response
res.redirect("/login");                   // 302 redirect
res.redirect(301, "/new-location");       // permanent redirect
res.set("X-Total", "100");                // set a header

A Complete Example

import express from "express";
const app = express();
app.use(express.json());

const users = [
  { id: 1, name: "Ada" },
  { id: 2, name: "Linus" },
];

app.get("/users", (req, res) => {
  res.json(users);
});

app.post("/users", (req, res) => {
  const user = { id: users.length + 1, ...req.body };
  users.push(user);
  res.status(201).json(user);
});

app.listen(3000);

Test with curl:

curl http://localhost:3000/users
# [{"id":1,"name":"Ada"},{"id":2,"name":"Linus"}]

curl -X POST http://localhost:3000/users \
  -H "content-type: application/json" \
  -d '{"name":"Grace"}'
# {"id":3,"name":"Grace"}

Up Next

Path parameters — /users/:id.

Route Parameters →