NodeJS

  • a JS runtime
    • built on Google’s open-source V8 JS engine
  • used to isolate JS from the client-side’s browser runtime
    • V8 engine runs the code on the server
    • making NodeJS a perfect web server
  • allows JS to be used as a server-side language
    • to build fast and highly scalable back-end network applications

Notable Characteristics

  • single-threaded, event-driven, non-blocking I/O model
    • makes NodeJS lightweight and efficient
  • allows for using JS throughout the stack
  • Node Package Manager (NPM): huge open-source packages for NodeJS available
  • good for building fast and scalable data-intensive applications

Applications

  • API with database
  • Data Streaming like YouTube
  • Real-Time Chat applications

  • Server-Side Web Applications

  • do not use NodeJS for heavy server-side processing
    • video conversions
    • file compressions
    • heavy image manipulation
  • for heavy server-side processing, use
    • Ruby
    • Python
    • PHP

Well-know Users of NodeJS

  • Netflix
  • UBER
  • PayPal
  • ebay

NodeJS Setup

Node REPL

  • REPL: Read-Eval-Print-Loop
    • the internal CLI of node
    • enter node in CLI after installing NodeJS on your system
  • javascript code can be run like in a CLI-based based environment
    • like IPython for instance

Sync vs. Async Code

  • synchronous code is also called blocking code
    • doesn’t execute the next command or line in script until current line completes execution
    • certain operations don’t execute unless the previous code has completed
  • asynchronous code is written to avoid this blocking
    • the future lines of code will be executed while current asynchronous code waits for execution to complete

Callback functions

  • these are an important part of asynchronous functions
  • callback functions are triggered at the end of execution of async function
  • using callbacks doesn’t automatically make a function asynchronous
    • only certain function have the callback functionality

Need for Asynchronous Code

  • NodeJS is single threaded
    • irrespective of whether 5 people are accessing the backend server or 5 million
  • so if millions of users are running synchronous code, the single thread is blocked to run the user requests in a queue
    • this would delay the response for all users
    • async code comes to the rescue in these situations
  • it is the responsibility of the NodeJS programmer to write asynchronous code to handle multiple users that scale up to millions
    • time consuming tasks must be made asynchronous functions to allow other faster requests to go through
    • callbacks can be used to automatically execute after the asynchronous function has completed execution