NODE.JS, APIs, AND AI INTEGRATION

What is Node.js?

V8 ENGINE · EVENT-DRIVEN · NON-BLOCKING I/O

📜 CODE BLOCK 1: First Steps — Installing and Running Node.js

// ============================================
// STEP 1: INSTALL NODE.JS
// ============================================
// Go to https://nodejs.org
// Download the LTS (Long Term Support) version
// Run the installer — it adds 'node' and 'npm' commands to your terminal

// ============================================
// STEP 2: VERIFY INSTALLATION (run in terminal)
// ============================================
// $ node --version
// Expected output: v18.x.x or higher
// $ npm --version
// Expected output: 9.x.x or higher

// ============================================
// STEP 3: CREATE A SIMPLE JAVASCRIPT FILE (hello.js)
// ============================================
// Create a file named hello.js with this content:

// WHY: console.log works the same in Node.js as in browsers
console.log("Hello from Node.js!");

// WHY: Node.js has a global object (like window in browsers)
// HOW: global is the root object in Node.js
global.console.log("This also works!");

// ============================================
// STEP 4: RUN THE FILE FROM TERMINAL
// ============================================
// Navigate to the folder containing hello.js
// Then run: $ node hello.js
// Output: Hello from Node.js!
//         This also works!
    

Creating an HTTP Server

HTTP MODULE · PORTS · REQUEST & RESPONSE

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

// ============================================
// COMPLETE WEB SERVER WITH NODE.JS
// ============================================

// WHY: The http module is built into Node.js for creating web servers
// HOW: require() imports built-in or third-party modules
const http = require("http");

// WHY: This array simulates a database of students in our course
// In a real app, this data would come from a database
const students = [
  { name: "Kemi", cohort: "01" },
  { name: "Tunde", cohort: "01" },
  { name: "Amara", cohort: "01" }
];

// WHY: createServer creates a new HTTP server
// HOW: The callback runs every time a request arrives
// req = request object (contains URL, headers, method, body)
// res = response object (used to send data back to client)
const server = http.createServer((req, res) => {
  
  // WHY: writeHead sets the HTTP status code and response headers
  // HOW: 200 means "OK" (request succeeded)
  // Content-Type tells the browser we're sending JSON data
  res.writeHead(200, { "Content-Type": "application/json" });
  
  // WHY: We need to send the response as a JSON string
  // HOW: JSON.stringify converts JavaScript objects to JSON text
  // The response object contains both course info and the students array
  const responseData = {
    course: "JS Mastery",
    students: students
  };
  
  // WHY: res.end sends the response and ends the connection
  // Without .end(), the browser would wait forever
  res.end(JSON.stringify(responseData));
});

// WHY: .listen() tells the server to start listening for connections
// HOW: 3000 is the port number (like a door number)
// The callback runs once the server is successfully listening
server.listen(3000, () => {
  console.log("Webbo3 server running on http://localhost:3000");
  // Open your browser and go to http://localhost:3000
  // You will see JSON data from our server!
});

// ============================================
// HOW TO RUN THIS FILE
// ============================================
// 1. Save this code as server.js
// 2. Open terminal in the same folder
// 3. Run: node server.js
// 4. You should see: "Webbo3 server running on http://localhost:3000"
// 5. Open your browser and visit http://localhost:3000
// 6. To stop the server: press Ctrl + C in the terminal
    

Understanding Port Numbers

DOOR NUMBERS · LOCALHOST · 3000 vs 80

Common Node.js Errors & Solutions

EADDRINUSE · MODULE NOT FOUND · SYNTAX ERRORS

🚫 ERROR: EADDRINUSE (Port already in use)

This means another application is already using port 3000. Solutions: (1) Change the port number in your code, (2) Find and kill the process using that port, or (3) Use a different port like 3001.

📁 ERROR: Cannot find module

Node.js cannot find the file you're trying to require. Check your file path and make sure the module is installed (npm install).

🟡 ERROR: SyntaxError

You have a typo in your code — missing parenthesis, bracket, or comma. The error message tells you the line number. Read it carefully!

📟 TERMINAL COMMANDS REFERENCE

# Check Node.js version
node --version

# Check npm version
npm --version

# Run a JavaScript file
node server.js

# Stop a running server (press Ctrl + C)
Ctrl + C

# List all processes using a port (Mac/Linux)
lsof -i :3000

# Kill a process by PID
kill -9 [PID]

🤖 HOW AI ACCELERATES THIS TOPIC

Ask AI: "I'm getting an EADDRINUSE error when running node server.js. What does this mean and how do I fix it?" Get immediate diagnosis.

Ask: "Explain the event loop in Node.js vs the browser event loop." Learn the core architecture difference.

Ask: "Write a Node.js server that serves an HTML file instead of JSON." Get production-ready code with proper Content-Type.