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Node.js Tutorial

Node.js is an open-source, cross-platform runtime environment that allows you to run JavaScript code on the server-side. It is built on Chrome's V8 JavaScript engine and is widely used for building scalable network applications.

1. Getting Started​

Installation​

  1. Download and install Node.js from nodejs.org.
  2. Verify installation: 
    node -v   # Check Node.js version
    npm -v    # Check npm version

Running Your First Script​

Create a file named app.js:

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

Run the file using:

node app.js

2. Core Concepts​

Global Objects​

Node.js provides several global objects like __dirname, __filename, and process.

console.log(__dirname);  // Directory of the current module
console.log(__filename); // Filename of the current module

REPL (Read-Eval-Print Loop)​

Start the Node.js REPL by typing node in the terminal.

node

You can run JavaScript expressions directly:

> 2 + 3
5

3. Modules​

Built-in Modules​

Node.js comes with built-in modules like fs, http, path, and more.

Example: Using the os module​

const os = require("os");
console.log(os.platform());
console.log(os.freemem());

Custom Modules​

Create a module:

// math.js
exports.add = (a, b) => a + b;
exports.subtract = (a, b) => a - b;

Use the module in another file:

const math = require("./math");
console.log(math.add(5, 3));

4. File System Operations​

Reading and Writing Files​

Use the fs module for file operations.

Reading a File​

const fs = require("fs");
fs.readFile("example.txt", "utf8", (err, data) => {
  if (err) throw err;
  console.log(data);
});

Writing to a File​

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

5. HTTP Server​

Creating a Simple Server​

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

6. Event Loop and Events​

Using Event Emitters​

const EventEmitter = require("events");
const emitter = new EventEmitter();

emitter.on("greet", () => {
  console.log("Hello, Event!");
});

emitter.emit("greet");

7. npm and Package Management​

Installing Packages​

Search for a package on npmjs.com.

Install a package:

npm install lodash

Use it in your project:

const _ = require("lodash");
console.log(_.capitalize("hello world"));

Managing Dependencies​

  • Install all dependencies from package.json: 
    npm install
  • Uninstall a package: 
    npm uninstall lodash

8. Express Framework​

Setting Up Express​

Install Express:

npm install express

Create a simple Express server:

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

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

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

9. Asynchronous Programming​

Callbacks​

fs.readFile("example.txt", (err, data) => {
  if (err) throw err;
  console.log(data.toString());
});

Promises​

const readFile = require("fs").promises.readFile;
readFile("example.txt", "utf8")
  .then(data => console.log(data))
  .catch(err => console.error(err));

Async/Await​

async function readFileAsync() {
  try {
    const data = await fs.promises.readFile("example.txt", "utf8");
    console.log(data);
  } catch (err) {
    console.error(err);
  }
}
readFileAsync();

10. Connecting to Databases​

Using MongoDB with Mongoose​

Install Mongoose:

npm install mongoose

Connect to MongoDB:

const mongoose = require("mongoose");

mongoose.connect("mongodb://localhost:27017/test", {
  useNewUrlParser: true,
  useUnifiedTopology: true
});

const db = mongoose.connection;
db.on("error", console.error.bind(console, "connection error:"));
db.once("open", () => {
  console.log("Connected to MongoDB");
});

Define a Schema and Model:

const schema = new mongoose.Schema({ name: String });
const Model = mongoose.model("Model", schema);

const doc = new Model({ name: "Node.js" });
doc.save().then(() => console.log("Document saved"));

Conclusion​

This tutorial covers the basics and core features of Node.js. Explore further by building projects and learning advanced topics like streams, clustering, and WebSockets.

Content Review​

The content in this repository has been reviewed by chevp. Chevp is dedicated to ensuring that the information provided is accurate, relevant, and up-to-date, helping users to learn and implement programming skills effectively.

About the Reviewer​

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