Node.js & Backend JavaScript

You are reading Part 39 of the 39-part series: JavaScript Skill Progression: The Path from Beginner to Extreme. [Level 6]

Introduction

JavaScript is traditionally known as a client-side language, but with Node.js, it can also be used for backend development. Node.js is a JavaScript runtime environment that allows developers to run JavaScript on the server, enabling high-performance applications, APIs, and real-time communication.

1. What is Node.js?

Node.js is a server-side runtime built on Google Chrome’s V8 JavaScript engine. It enables non-blocking, event-driven programming, making it highly efficient for I/O-intensive tasks.

Key Features of Node.js:

• Asynchronous & Non-blocking – Handles multiple requests concurrently.

• Single-threaded Event Loop – Uses an event-driven architecture for efficiency.

• Built-in Modules – Includes modules like fs, http, and crypto.

• Package Management with NPM – Provides access to thousands of libraries.

Example: Running JavaScript in Node.js

console.log("Hello from Node.js!");

To run the script:

node script.js

2. Setting Up a Node.js Server

A basic Node.js server can be created using the built-in http module.

Example: Simple HTTP Server

const http = require("http");

const server = http.createServer((req, res) => {
    res.writeHead(200, { "Content-Type": "text/plain" });
    res.end("Hello, Node.js Server!");
});

server.listen(3000, () => console.log("Server running on http://localhost:3000"));

• Runs a server on port 3000.

• Responds with "Hello, Node.js Server!".

3. Understanding the Node.js Event Loop

Node.js uses an event-driven architecture where callbacks are managed by an event loop.

Example: Asynchronous vs. Synchronous Execution

console.log("Start");
setTimeout(() => console.log("Timeout callback"), 1000);
console.log("End");

Output:

Start
End
Timeout callback (after 1 second)

• Synchronous code runs first.

• Asynchronous tasks are pushed to the event loop and executed later.

4. File System Operations in Node.js

Node.js allows direct interaction with the file system using the fs module.

Example: Reading a File

const fs = require("fs");

fs.readFile("file.txt", "utf8", (err, data) => {
    if (err) throw err;
    console.log("File Contents:", data);
});

Example: Writing to a File

fs.writeFile("output.txt", "Hello, Node.js!", (err) => {
    if (err) throw err;
    console.log("File written successfully");
});

5. Using Express.js for Backend Development

Express.js is a popular framework for building REST APIs with Node.js.

Example: Simple Express Server

const express = require("express");
const app = express();

app.get("/", (req, res) => {
    res.send("Hello from Express!");
});

app.listen(3000, () => console.log("Express server running on http://localhost:3000"));

• Handles HTTP requests using app.get().

• Runs on port 3000.

6. Connecting Node.js to a Database (MongoDB)

Node.js can connect to databases like MongoDB using libraries like Mongoose.

Example: Connecting to MongoDB

const mongoose = require("mongoose");

mongoose.connect("mongodb://localhost:27017/testdb", { useNewUrlParser: true, useUnifiedTopology: true })
    .then(() => console.log("Connected to MongoDB"))
    .catch(err => console.error("MongoDB Connection Error:", err));

Example: Defining a Schema and Saving Data

const UserSchema = new mongoose.Schema({ name: String, age: Number });
const User = mongoose.model("User", UserSchema);

const newUser = new User({ name: "Alice", age: 30 });
newUser.save().then(() => console.log("User saved"));

7. Real-Time Communication with WebSockets

Node.js enables real-time applications using WebSockets.

Example: WebSocket Server with Socket.io

const io = require("socket.io")(3000);

io.on("connection", socket => {
    console.log("New client connected");
    socket.on("message", msg => console.log("Message received:", msg));
});

8. When to Use Node.js?

You are reading Part 39 of the 39-part series: JavaScript Skill Progression: The Path from Beginner to Extreme. [Level 6]