Routing

This lesson covers Routing. If this feels new, that is normal. We will build up slowly.

What you will learn

• What routing means — in normal words, not textbook words
• How it works step by step
• Code you can run today on your laptop
• Where teams use this in real projects

Before you start

• Software: Node.js LTS from nodejs.org, VS Code, and a terminal
• Knowledge: Earlier lessons in this Node.js course
• Previous lesson: Express Setup — Complete Guide

Explain it simply

Routing maps a URL and HTTP method to a function. GET /users runs a different handler than POST /users.

Why developers use this

• Core skill for web backends
• Huge community and docs
• Leads to REST and auth

How it works (step by step)

1. A browser or app sends an HTTP request to your server.
2. Express middleware runs in order (log, parse JSON, check auth).
3. The route handler for Routing runs your logic.
4. You send JSON or HTML back with the right status code (200, 201, 404, 500).

Code example — type this yourself

app.get('/users', (req, res) => res.json(users));
app.get('/users/:id', (req, res) => {
  const user = users.find((u) => u.id === req.params.id);
  res.json(user || { error: 'Not found' });
});

:id is a route parameter — available as req.params.id. Return 404 when nothing matches.

What each part does

• app.get('/users', (req, res) => res.json(users)); — Sends the response back to the client.
• app.get('/users/:id', (req, res) => { — Defines what happens when a client hits this URL and HTTP method.
• const user = users.find((u) => u.id === req.params.id); — Line 3: runs as written.
• res.json(user || { error: 'Not found' }); — Sends the response back to the client.
• }); — Line 5: runs as written.

Real life: where Routing shows up

A college admin panel uses Routing with Express: students hit /courses, teachers hit /grades, and shared middleware checks login once for every page.

Try it yourself — hands-on

1. Create a new file (e.g. routing-demo.js) in an empty folder
2. Type the example code for Routing yourself — typing helps memory
3. Run node on that file and read the output
4. Change one line (a value, a message, a route path) and run again to see what breaks or improves

Common mistakes (avoid these)

• Skipping the terminal — Routing only feels easy after you run code yourself.

Interview note

Be ready to explain Routing with a real trade-off: what problem it solves and what you would not use it for.

Summary

• You can explain Routing in your own words
• You ran working code — not just read about it
• You know one mistake to avoid and one real place teams use this