Building a REST API with Express

What is Express?

MINIMAL · FLEXIBLE · NODE.JS WEB FRAMEWORK

📜 CODE BLOCK 1: Install Express (run in terminal)

// ============================================
// STEP 1: Create project and install Express
// ============================================

// Create a new directory for your API project
mkdir webbo3-api
cd webbo3-api

// Initialize npm project
npm init -y

// Install Express (saves to dependencies)
npm install express

// For development, you might also want nodemon (auto-restart)
npm install --save-dev nodemon

// Update package.json scripts:
// "scripts": {
//   "start": "node app.js",
//   "dev": "nodemon app.js"
// }
    

Complete Express Server

GET · POST · JSON MIDDLEWARE · ROUTING

📜 CODE BLOCK 2: Complete app.js (with line-by-line comments)

// ============================================
// COMPLETE REST API WITH EXPRESS
// ============================================

// WHY: Import the express framework
// HOW: require() loads the express module from node_modules
const express = require("express");

// WHY: Create an Express application instance
// This app object has methods like .get(), .post(), .listen()
const app = express();

// WHY: This middleware parses incoming JSON request bodies
// Without this, req.body would be undefined for POST requests
// .use() tells Express to use this middleware for every request
app.use(express.json());

// ============================================
// DATA (simulating a database)
// ============================================
// WHY: In-memory array acts as our data store
// In production, this would be a real database like MongoDB or PostgreSQL
const students = [
  { id: 1, name: "Kemi", skill: "JavaScript" },
  { id: 2, name: "Tunde", skill: "React" },
  { id: 3, name: "Amara", skill: "Node.js" }
];

// ============================================
// ROUTE 1: GET / (Home/Welcome route)
// ============================================
// WHY: The root endpoint returns a welcome message
// HOW: app.get() handles HTTP GET requests to the specified path
// req: request object (contains query params, headers, body)
// res: response object (used to send data back to client)
app.get("/", (req, res) => {
  // res.json() automatically sets Content-Type to application/json
  // It also stringifies the JavaScript object for you
  res.json({ message: "Welcome to Webbo3 API" });
});

// ============================================
// ROUTE 2: GET /students (Read all students)
// ============================================
// WHY: This endpoint returns the entire list of students
// REST standard: GET for reading data
app.get("/students", (req, res) => {
  // Send the students array as JSON
  res.json(students);
});

// ============================================
// ROUTE 3: POST /students (Create a new student)
// ============================================
// WHY: This endpoint adds a new student to our data store
// REST standard: POST for creating new resources
// The client sends the new student data in the request body
app.post("/students", (req, res) => {
  // Extract the new student data from the request body
  // req.body is populated by express.json() middleware
  const newStudent = {
    id: students.length + 1,  // Auto-increment ID
    ...req.body        // Spread operator merges name and skill
  };
  
  // Add the new student to our array
  students.push(newStudent);
  
  // Send back the created student with HTTP status 201 (Created)
  // 201 is the standard status code for successful resource creation
  res.status(201).json(newStudent);
});

// ============================================
// START THE SERVER
// ============================================
// WHY: .listen() binds the server to a port and starts listening
// Port 3000 is the standard development port for Express
app.listen(3000, () => {
  console.log("API running on port 3000");
  console.log("Test GET: http://localhost:3000/students");
  console.log("Test POST: Use Thunder Client or curl");
});

// ============================================
// HOW TO RUN
// ============================================
// $ node app.js
// OR with nodemon (auto-restart on changes):
// $ npx nodemon app.js
    

Testing Your API

THUNDER CLIENT · CURL · BROWSER

✅ TEST YOUR API

Method 1: Browser (GET only)
Open http://localhost:3000/students in your browser. You will see the JSON data.

Method 2: curl in terminal (GET)
curl http://localhost:3000/students

Method 3: curl for POST (create a student)
curl -X POST http://localhost:3000/students -H "Content-Type: application/json" -d '{"name":"Zainab","skill":"Python"}'

Method 4: Thunder Client (VS Code extension)
Install Thunder Client extension, create a new request, select GET or POST, enter URL, and send.

What Makes an API RESTful?

RESOURCE-BASED · STATELESS · STANDARD HTTP METHODS

🤖 HOW AI ACCELERATES REST API DEVELOPMENT