Why Express?

Node.js gives you low-level tools to work with HTTP.

Express sits on top of Node and makes it easier to:

• create servers
• define routes
• handle requests and responses
• organize backend code

Express helps you focus on what your API does, not boilerplate.

Creating Your First Express Server

Install Express:

npm install express

Create a basic server:

import express from "express";

const app = express();

app.get("/", (req, res) => {
  res.json({ message: "Hello Express" });
});

app.listen(3000, () => {
  console.log("Server running on port 3000");
});

Visit http://localhost:3000 in your browser.

Request & Response (Mental Model)

Every request follows this flow:

Client → Request → Server → Response → Client

The animation above shows how a request enters your server, hits a route, and returns a response.

Routing Basics

Routes are defined by:

• HTTP method
• URL path

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

app.post("/users", (req, res) => {
  res.json({ created: true });
});

Each route handles one responsibility.

Route Parameters

app.get("/users/:id", (req, res) => {
  const userId = req.params.id;
  res.json({ userId });
});

Dynamic routes let you work with specific resources.

Interactive Exercise: Route Matching

Try this:

• Define different routes
• Change the URL
• Observe which route matches

Quick Exercise (Offline)

• Create /users and /products routes
• Add one route with a URL parameter
• Return JSON from every route