JavaScript in Node.js

What You’ll Learn 📚

• Introduction to Node.js and its purpose
• Core JavaScript concepts in a Node.js environment
• Practical examples from simple to complex
• Common questions and troubleshooting tips

Introduction to Node.js

Node.js is a powerful runtime environment that allows you to run JavaScript on the server side. It uses the V8 JavaScript engine, which is the same engine that powers Google Chrome. This means you can use JavaScript to build everything from simple scripts to complex web applications. 🌐

Node.js is often used for building scalable network applications due to its non-blocking, event-driven architecture.

Key Terminology

• Runtime Environment: A platform that allows code to be executed outside of a browser.
• V8 Engine: Google’s open-source high-performance JavaScript and WebAssembly engine.
• Event-driven: A programming paradigm where the flow of the program is determined by events such as user actions or messages from other programs.

Getting Started with Node.js

Before we jump into code, let’s make sure you have Node.js installed on your machine. Follow these steps to set it up:

1. Visit the Node.js official website and download the LTS version.
2. Run the installer and follow the instructions.
3. Verify the installation by opening your terminal and typing:

node -v

If you see a version number, you’re all set! 🎉

Simple JavaScript Example in Node.js

// hello.js
console.log('Hello, Node.js!');

node hello.js

Progressively Complex Examples

Example 1: Basic HTTP Server

// server.js
const http = require('http');

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

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

node server.js

Example 2: Reading a File

// readFile.js
const fs = require('fs');

fs.readFile('example.txt', 'utf8', (err, data) => {
  if (err) {
    console.error(err);
    return;
  }
  console.log(data);
});

node readFile.js

Example 3: Using Modules

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

// app.js
const math = require('./math');
console.log(math.add(2, 3));

node app.js

Common Questions and Answers

1. What is Node.js used for?

   Node.js is used for building scalable network applications, real-time applications, and more. It’s popular for its non-blocking, event-driven architecture.

2. How does Node.js handle multiple requests?

   Node.js uses an event-driven, non-blocking I/O model, allowing it to handle multiple requests efficiently without waiting for one to complete before starting another.

3. Why use JavaScript on the server side?

   Using JavaScript on the server side allows for a unified language across both client and server, simplifying the development process and enabling code reuse.

4. What is npm?

   npm is the package manager for Node.js, used to install and manage libraries and dependencies for your projects.

5. How do I handle errors in Node.js?

   Errors in Node.js can be handled using try-catch blocks, error-first callbacks, or promises and async/await for asynchronous code.

Troubleshooting Common Issues

If you encounter an error saying ‘command not found’ when running Node.js commands, ensure Node.js is installed correctly and your PATH environment variable is set up properly.

Here are some common issues and how to resolve them:

• Issue: ‘EADDRINUSE’ error when starting a server.
  Solution: This means the port is already in use. Try using a different port number.
• Issue: ‘MODULE_NOT_FOUND’ error.
  Solution: Ensure the module name is correct and the module is installed. Use npm install module-name if needed.

Practice Exercises

Try these exercises to reinforce your learning:

1. Create a Node.js script that writes ‘Hello, File!’ to a new file named output.txt.
2. Modify the HTTP server example to respond with a JSON object instead of plain text.
3. Build a simple calculator module that supports addition, subtraction, multiplication, and division.

Remember, practice makes perfect! Keep experimenting and don’t hesitate to explore the Node.js documentation for more information. Happy coding! 😊