Unit 1: Node.js backend foundations

Node.js is a JavaScript runtime built on Chrome's V8 engine that runs JavaScript on the server. It is single-threaded and event-driven with non-blocking I/O, which makes it efficient for many simultaneous connections.

• npm (Node Package Manager): npm init -y, npm install express, scripts in package.json.
• Modules: built-in (fs, http, path), local (require("./math") or ES import) and third-party (from npm).
• REPL: an interactive shell (type node) for testing code.
• File system: fs.readFile, fs.writeFile, fs.appendFile and their promise versions.

javascriptconst fs = require("fs/promises");
async function readNotes() {
  try {
    const text = await fs.readFile("notes.txt", "utf8");
    console.log(text);
  } catch (err) {
    console.error("Could not read file", err);
  }
}

javascriptconst express = require("express");
const app = express();
app.use(express.json());                        // middleware: parse JSON bodies
app.use((req, res, next) => {                   // custom logging middleware
  console.log(req.method, req.url); next();
});
app.get("/api/tasks", (req, res) => res.json(tasks));
app.post("/api/tasks", (req, res) => { tasks.push(req.body); res.status(201).json(req.body); });
app.put("/api/tasks/:id", (req, res) => { /* update */ });
app.delete("/api/tasks/:id", (req, res) => { /* delete */ });
app.listen(5000, () => console.log("Server on 5000"));

Middleware is a function with access to req, res and next that runs between the request and the route handler — used for parsing, logging, authentication and error handling.

Test each endpoint with Postman: choose the method, URL, headers and JSON body, then check the status and response. Connect to MongoDB with Mongoose (Task.find(), Task.create()) or to MySQL with the mysql2 package.