JS's scope chain and closure

1.JS no block-level scope

    <Script>        functionMain () {if (1==1){                varname= "Alex";        } console.log (name);    } Main (); </Script>
Execution result: {} is a block-level scope.

Alex

2.JS takes a function as a scope chain

 <  script         >  function   Main () { var   Innervalue  =  "  alex  "  ;        } Main ();    Console.log (Innervalue);  </ script  > 
 Execution Result: 
  

Uncaught Referenceerror:innervalue is not defined

The scope chain for 3.JS has been generated before it was created

Example one:

    <Script>XO= "Alex"; functionFunc () {varXO= "Seven"; functioninner () {console.log (XO); }            returninner; }        varret=Func ();    RET (); </Script>
Execution result: The generated scope chain is XO ("Alex")----xo ("undefined")----XO (using the scope chain)

Seven

Example two:

    <Script>XO= "Alex"; functionFunc () {varXO= "Eric"; functioninner () {console.log (XO); } XO= "Seven"; returninner; }        varret=Func ();    RET (); </Script>
Execution result: The generated scope chain XO ("Alex")----xo ("undefined")----xo ("undefined")----Func[xo] ("Eric")----Func[xo] ("seven")----inner ()

Seven

Example three:

    <Script>XO= "Alex"; functionBar () {console.log (XO); }        functionFunc () {varXO= "Seven"; returnBar; }        varret=Func ();    RET (); </Script>
Execution result: The scope chain is divided into two segments: 1.xo ("Alex")----XO
2.xo ("Alex")----xo ("undefined")----Func[xo] ("seven")

Alex

Closures: If each of the downloaded JS has a custom global variable, then the import will occur when the mutual coverage of the phenomenon, through the closure can be locked into the function of the variable.

(function () {    var a = 123;    Function F1 () {        console.log (a);    }    function F2 () {        cocnsole.log (a);    }}) ();    

Object-oriented JS

    <Script>        functionFoo (name,age) { This. Name=name;  This. Age=Age ; } Foo.prototype={GetInfo:function(){                return  This. Name+  This. Age; }, Func:function(ARG) {return  This. Name+Arg; }        }        varobj= NewFoo ('Alex', A);        Console.log (Obj.name); Console.log (obj.        GetInfo ()); Console.log (obj. Func ( -)); </Script>
Execution Result:

Alexalex22alex55

JS's scope chain and closure