An Absolute understanding of basic of Node.js: Guide

Why Node.js?

JavaScript Blocking I/O

JavaScript Non-blocking I/O

  1. Push main() onto the call stack.
  2. Push console.log() onto the call stack. This then runs right away and gets popped.
  3. Push setTimeout(2000) onto the stack. setTimeout(2000) is a Node API. When we call it, we register the event-callback pair. The event will wait 2000 milliseconds, then callback is the function.
  4. After registering it in the APIs, setTimeout(2000) gets popped from the call stack.
  5. Now the second setTimeout(0) gets registered in the same way. We now have two Node APIs waiting to execute.
  6. After waiting for 0 seconds, setTimeout(0) gets moved to the callback queue, and the same thing happens with setTimeout(2000).
  7. In the callback queue, the functions wait for the call stack to be empty. Because only one statement can execute a time. This is taking care of by the event loop.
  8. The last console.log() runs, and the main() gets popped from the call stack.
  9. The event loop sees that the call stack is empty and the callback queue is not empty. So it moves the callbacks (in a first-in-first-out order) to the call stack for execution.



  • Node.js loads modules that come bundled with Node.js like the file system and HTTP from the Node.js API.
  • It loads third-party libraries like Express and Mongoose that you install from npm.
  • It lets you require your own files and modularize the project.

Node Modules

V8 turbo-charges JavaScript by leveraging C++


  • System Events: C++ core from a library called libuv. (For example, finished reading a file).
  • Custom Events: JavaScript core.




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