notes

Contents:
Callback
What's the callback? - call stack, WebAPI, event loop, queue
Use & its purpose of the callback
Pain of callback
Session reference  - http://latentflip.com/loupe/
---------------------------------------------------------------------------
MRF , Addeventlistener
array.map(()=>{
                                           
})
div.Addeventlistener("click",()=>{

})

callback:- It is a function which uses one more function as a parameter.(map,Addeventlistener).
Javascript:- single threaded can execute single task at a time.
synchronous:- It will execute all the code line by line in the order in which it is written.
Asynchronous :- It will do the task without waiting for a task to complete its execution. 

1.callstack:- 
It is place in browser where it keeps track of the function that has to be called in the program. 
It will execute whatever the statements inside it.

2.WebApis :- it is the place where the Asynchronous operations are actually executed.

3.queue :-
Queue is a datastructure , FIFO  
it stores the async function which has to be executed next.

4.Eventloop :-
It is between call stack as well as the event queue.
The main role of the event loop is to check whether the call stack is empty or not.
if it is empty it will push the code from queue and pass it to call stack
the call stack executes the function

pain of callback => callback Hell
(()=>{
  (()=>{
    
  })  
})