Introduction to Node.js

What is Node.js?

Node.js is a powerful, open-source, cross-platform JavaScript runtime environment that executes JavaScript code outside of a web browser. Built on the V8 JavaScript engine (the same engine used by Google Chrome), Node.js allows developers to use JavaScript for server-side scripting, enabling the creation of dynamic web pages and applications.

Why Use Node.js?

• Single Programming Language: With Node.js, you can use JavaScript both on the client side and server side, reducing the complexity of using multiple languages in a project.
• High Performance: Node.js is built on the V8 engine, which compiles JavaScript directly into machine code, making it fast and efficient.
• Non-blocking I/O: Node.js uses an event-driven, non-blocking I/O model, which makes it lightweight and efficient, ideal for data-intensive real-time applications.
• Scalability: Node.js is well-suited for building scalable network applications due to its asynchronous nature.

Core Concepts in Node.js

1. Asynchronous Programming

Node.js uses asynchronous programming to handle operations like reading from or writing to a file, making HTTP requests, or interacting with a database. Asynchronous programming means that the program doesn't wait for an operation to complete before moving on to the next one.

Example:

const fs = require("fs");

console.log("Start reading a file...");
fs.readFile("example.txt", "utf8", (err, data) => {
  if (err) {
    console.error(err);
    return;
  }
  console.log(data);
});
console.log("File reading started...");

2. Event Loop

The event loop is the heart of Node.js. It's a mechanism that handles asynchronous operations by allowing Node.js to perform non-blocking I/O operations. The event loop continuously checks the event queue to see if there are any events to process.

3. Modules

Node.js uses modules to manage code in separate files and folders. Modules are JavaScript libraries that can be included in a project using require().

Example:

// math.js
function add(a, b) {
  return a + b;
}

module.exports = { add };

// main.js
const math = require("./math");

console.log(math.add(2, 3)); // Output: 5

4. npm (Node Package Manager)

npm is the default package manager for Node.js. It allows developers to install and manage external libraries and tools that can be used in Node.js applications.

• Installing a Package:

  npm install express
  

• Creating a package.json File:

  npm init
  

5. HTTP Server

Node.js can be used to create a simple HTTP server that listens to client requests and sends back responses.

Example:

const http = require("http");

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader("Content-Type", "text/plain");
  res.end("Hello World\n");
});

server.listen(3000, "127.0.0.1", () => {
  console.log("Server running at http://127.0.0.1:3000/");
});

6. Express.js

Express.js is a popular web framework built on top of Node.js. It simplifies the process of building web applications and APIs by providing a robust set of features for web and mobile applications.

Example:

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

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

app.listen(3000, () => {
  console.log("Server is running on port 3000");
});

When to Use Node.js?

Node.js is ideal for building:

• Real-time applications (e.g., chat applications, online gaming)
• API servers (e.g., RESTful APIs)
• Single Page Applications (SPAs)*
• Microservices
• Data-intensive applications that need to handle a large number of requests

Homework:

• Set up Node.js on your machine.
• Create a simple Node.js application that reads a file asynchronously and prints its content to the console.
• Explore the npm website (https://www.npmjs.com/) and find a package that could be useful for your next project.