Node.js Lecture Notes

Introduction to Node.js

• Definition: Node.js is an open-source, cross-platform runtime environment for executing JavaScript code outside of a browser.
• Purpose: Used to build back-end services (APIs) that power client applications (web apps, mobile apps).

Benefits of Using Node.js

• Simplicity: Easy to get started, great for prototyping and agile development.
• Speed: Scalable and fast; used by companies like PayPal, Uber, Netflix, Walmart.
  • Example: PayPal's transition to Node.js reduced development time, lines of code, and improved requests served per second.
• JavaScript Reuse: Allows front-end developers to utilize JavaScript on the back end, leading to cleaner, more consistent code.
• Ecosystem: Largest ecosystem of open-source libraries.

Node.js Architecture

• Runtime Environment: Contains a JavaScript engine and objects for file system access, network communication, etc.
• Comparison with Browsers: Traditional JS runs in browsers (with engines like V8 in Chrome) providing a specific runtime environment.
• Differences: Node.js provides a non-blocking/non-synchronous architecture, allowing multiple operations simultaneously.

Node.js Non-blocking and Asynchronous Nature

• Metaphor: Restaurant analogy used
  • Non-blocking: Waiter takes order and serves multiple tables simultaneously.
  • Blocking: Waiter waits at kitchen for food before serving another table.
• Asynchronous Architecture: Single thread handles multiple requests without waiting for I/O operations to complete.

CPU Intensive Applications

• Limitation: Node.js is not recommended for CPU-intensive applications due to its single-threaded nature.

Installation of Node.js

1. Check existing node version with node --version.
2. Download the latest stable version from Node.js.
3. Install and confirm installation by checking the version again.

Building a Simple Node Application

• Create a new directory for the app.
• Use Visual Studio Code as the code editor.
• Write a basic JavaScript function to log a message to the console.
• Run the application using node app.js.

Node.js Module System

• Modules: Encapsulation of code to prevent polluting the global scope.
• Each file in Node.js is a module; variables defined in a module are private.
• Exporting and Importing: Use module.exports to make variables/functions public.

Built-in Node.js Modules

• Global Objects: console, setTimeout, clearTimeout, etc.
• Example of using FS module: To work with file systems (asynchronous operations recommended).

Event Handling in Node.js

• Event Emitter: Core building block in Node.js for responding to events.
  • Use on to attach a listener to an event and emit to raise an event.
• Callback Functions: Use alongside asynchronous methods for operations completion.

HTTP Module

• Built-in module for creating web servers.
• The server listens for incoming requests and responds accordingly.
  • Use createServer() to create an HTTP server and define request handling logic.
• Express Framework: Recommended for building complex applications instead of using the HTTP module directly.

Conclusion

• The lecture helps understand the basics of Node.js, its advantages, architecture, module system, event handling, and how to create a simple web server.
• Further learning involves deep diving into Express, MongoDB, unit testing, and other real-world applications.