Unit 3: Backend development and databases

Node.js runs JavaScript on the server; Express.js is a lightweight framework for building web servers and APIs on Node.

javascriptconst express = require("express");
const app = express();
app.use(express.json());                 // parse JSON bodies

app.get("/students", (req, res) => {     // GET route
  res.json([{ roll: 1, name: "Ana" }]);
});
app.post("/students", (req, res) => {    // POST route
  const s = req.body;
  res.status(201).json({ message: "Created", student: s });
});
app.listen(3000);

Routing maps a URL and HTTP method to a handler function. Route parameters (/students/:id) read values from the URL.

Express uses middleware such as express-session and cookie-parser; PHP uses session_start() and $_SESSION. Sessions keep users logged in across requests; cookies store a session ID in the browser.

CRUD = Create, Read, Update, Delete — the four basic data operations.

php<?php
$conn = new mysqli("localhost", "root", "", "college");
$stmt = $conn->prepare("INSERT INTO student (name, course) VALUES (?, ?)");
$stmt->bind_param("ss", $name, $course);   // prepared statement prevents SQL injection
$stmt->execute();
?>

JSON is the standard data format for APIs: {"roll": 1, "name": "Ana", "courses": ["BCA"]}. A REST API exposes resources at URLs and uses HTTP methods to act on them, returning JSON and status codes.