Express.js

Build real HTTP servers fast with Express. Learn routing, middleware composition, JSON body parsing, and serving static files.

ExpressroutingmiddlewareREST

Duration

⏱ About 2 hours

Level

📊 Intermediate

Prerequisite

🎯 node-03

OUTCOME

An Express server with multiple routes, middleware, and static assets

What you'll learn

1Set up an Express app and route handlers
2Use built-in JSON and static middleware
3Write custom middleware (logging, auth check)
4Handle errors centrally

1. Hello, Express

bash

npm install express

javascript

import express from "express";
const app = express();

app.get("/", (req, res) => {
  res.send("Hello from Express!");
});

app.get("/api/hello/:name", (req, res) => {
  res.json({ message: `Hello, ${req.params.name}!` });
});

app.listen(3000, () => console.log("http://localhost:3000"));

2. Middleware

javascript

// Built-in: parse JSON bodies
app.use(express.json());

// Built-in: serve files from /public
app.use(express.static("public"));

// Custom: log every request
app.use((req, res, next) => {
  console.log(`${req.method} ${req.url}`);
  next();
});

Middleware runs in the order it is registered. Always call next() unless you send a response.

3. Route Methods

javascript

app.post("/users", (req, res) => {
  const user = req.body;       // populated by express.json()
  // ... save to database ...
  res.status(201).json(user);
});

app.put("/users/:id", (req, res) => { /* ... */ });
app.delete("/users/:id", (req, res) => { /* ... */ });

4. Error Handling

javascript

// 404 (no route matched)
app.use((req, res) => {
  res.status(404).json({ error: "Not found" });
});

// Error middleware (4 args!)
app.use((err, req, res, next) => {
  console.error(err);
  res.status(500).json({ error: "Internal server error" });
});

⚠️

Error middleware must have 4 parameters (err, req, res, next) — that signature is how Express recognizes it.

Example code / lecture materials

All lecture materials and example code are openly available on GitHub.

View on GitHub ↗