NodeJS: Runtime Environment and Event-Driven Model

• NodeJS
  • Is an application framework
  • Is a runtime environment that allows JavaScript execution on the server side
  • Created by Ryan Dahl
  • Can build fast and interactive web applications needing live updates, like chat apps using WebSockets
  • Is an open-source, cross-platform runtime environment for server-side and networking applications
  • Uses an event-driven, non-blocking I/O model
  • This approach makes NodeJS lightweight and efficient
  • Is ideal for data-intensive, real-time applications across distributed devices

Event-Driven Model

• Its flow of execution is determined by events, not sequential execution
• Works through:
  • System listening for events
  • When an event occurs, a callback function (event handler) executes without blocking execution
  • Which makes event-driven systems more responsive and efficient
• Key components:
  • Event emitter
  • Event listener
  • Callback function

Event Loop

• Is a core mechanism in Node.js
• Handles multiple operations without blocking execution
• Makes Node.js fast and efficient for real-time applications

Use Cases

• Not the best platform for CPU-intensive heavy computational applications
• Ideal for building fast and scalable network applications
• Capable of handling numerous simultaneous connections with high throughput
• For each connection, NodeJS doesn't spawn a new thread, which prevents maxing out memory
• Instead, it handles all connections in a single thread using a non-blocking I/O model
• Has achieved over 1 million concurrent connections
• Bubbling errors up to the NodeJS core event loop will cause the entire program to crash
• Suitable for I/O bound, data streaming, and data-intensive real-time applications
• Also suitable for JSON APIs and single-page applications

Advantages

• Can use a single programming language from one end of the application to the other
• NodeJS applications are easily scalable horizontally and vertically
• Delivers improved performance because the V8 engine compiles JS code into machine code directly
• Performance also increases by caching modules into memory after their first use
• Is easily extensible
• Supports common tools like unit testing
• Has a well-built 'npm' package manager with many reusable modules

Disadvantages

• The number of robust libraries is comparatively low, even though there are a number of libraries available
• Is not suitable for computationally intensive tasks
• The asynchronous programming model is more complex compared to the synchronous model

NodeJS Package Manager

• Reusable NodeJS components are easily available through an online repository
• It is built-in with dependency management, version, and scripting mechanisms
• Global installations are available throughout the system
• Local installations are available for the specific application
• By default, all dependencies are installed in the 'node_modules' directory
• 'package.json' contains all information related to the NodeJS application
• The 'package.json' file should be placed in the root directory of the application
• The 'package.json' file contains the name, version, author, repository, required node version, scripts, dependencies, etc

Package manager version number contraints:

• <= Installs the specified version or lower
  • "express": "<=4.18.2" will install version 4.18.2 or lower

• = Installs the specified version or higher

  • "express": ">=4.18.2" will install version 4.18.2 or higher
• ~ Allows only patch updates
  • "express": "~4.18.2" allows updates like 4.18.x but not 4.19.0
• ^ Allows minor & patch updates
  • "express": "^4.18.2" allows updates like 4.x.x but not 5.0.0
• * Installs any available version
  • "express": "*" installs any available version, though this is not recommmended
• 1.2.x Installs any patch version
  • "express": "1.2.x" will install versions like 1.2.0 and 1.2.5, but not 1.3.0
• latest Installs the latest available version
  • “express": "latest" installs the most recent version from npm
• Dependencies are needed in runtime
  • e.g., express, mongoose
• devDependencies are only needed for development
  • e.g., jest, nodemon

Node Require

• require() is a built-in function in Node.js
• Imports modules and files
• Require modules get loaded synchronously and will be cached after the first use
• A core module in Node.js is built-in and comes with Node.js
  • Core modules are required like this: const http = require('http');
• Modules starting with ./, ../, or / are treated as local files/modules
  • Local modules are included like this: const add = require('./math');