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JavaScript Decoded :check: (Neeem), JavaScriptRuntime Env Components -…

- - - - Created for Window Object
    - - Created for each Function
    - - Created for Keywords
        let and const
- - - - When Const Var is assinged new value
    - - Incorrect syntax
        eg: duplicate declaration
      - if without statements
    - - var 'x' not defined
  - - - Prog with var
        function printNumAfterXSeconds()
        {
        for(let i =1 ; i<= 5; i++){
        setTimeout(function(){
        console.log('i is', i); }
        , i*1000);
        }
        }
        
        o/p:6,6,6,6,6
        Reason: var i inceamented to 6
        and closure has ref to i.
        Since var keyword has global scope
      - Prog with let
        function printNumAfterXSeconds()
        { for(let i =1 ; i<= 5; i++)
        { setTimeout(function()
        { console.log('i is', i);
        }, i*1000);
        }
        }
        o/p: 1,2,3,4,5
        Reason: let i inceamented by 1
        and closure has ref to i
        let keyword makes sure that i has block scope
    - - Currying
      - Module Pattern
      - DataHiding/ Encapsulation
    - - Memory Usage is High
        since var/parms are not garbage collected.
        In Example of outer and inner fucntions
        var num1 is not garbage collected since inner function uses it
      - Memory Leaks
  - - - Function Statement/ Declaration
        
        function add(){
        console.log(Function Statement);
        }
        
        During Hoisting memory created for Fucntion statement
      - Function Expression
        
        var sum = function (){
        console.log(Function Expression);
        }
        
        During Hoisting memory is NOT created for Fucntion Expression
      - Anonymous
        
        function(){ console.log('anonymous'); }
        
        Functions used as VALUES
      - NamedFunctionExpression
        
        var sum = add(n1,n2)
        { return n1+n2 ;}
        
        In above eg: sum is NamedFunctionExpression
        sum(n1,n2); is valid invocation but
        add(n1,n2); is invalid since add is not hoisted in
        global scope
      - FirstClassFunction
        FirstClassCitizens
        
        When functions are used
        as arguments to other function or
        when function is returned from other function
        eg1: function process(fuction success(){} ,
        function failure(){})
        eg2: function counter(){
        var count =0;
        return function(){
        return count++; }
        }
      - ArrowFunction
      - Callback
        
        In below functions x and y,
        function defn of y is passed
        as argument to function x
        
        function x(y)
        {console.log('in x'); y();}
        x(function y(){
        console.log('in callback funct y');
        })
        
        "I will call back later!"
        A callback is a function passed
        as an argument to another function.
        This technique allows a function
        to call another function.
        A callback function can run
        after another function has finished
- - - - Parses your syntax
        using Syntax Parser
      - Creates AST
        Abstract Syntax Tree
        and Passes to Compilation phase
        to See AST : astexplorer.net
    - - JIT Compiler
        Just in Time
      - AOT Compiler
        Ahead of time
      - Creates optimized code using JIT or AOT