You think you know a lot about javascript? (Personal answer)

Code Source:http://www.ido321.com/914.html

Code Source:http://dmitry.baranovskiy.com/post/91403200

Pure personal understanding, Welcome to the Great God,

1.

1     if inch window)) {23         var a = 1; 4 5     }67     alert (a);  // undefined

There is no block-level scope in JS, so a will declare in advance that "a" in window will get true, so a is not assigned a value operation

2.

1     var a = 1,23         function  A (x) {45             x && A (--x); 6 7         }; 8 9     // 1

First, refer to the following code

1 var function g () {2// eject G's function body 3}; 4 alert (g);  // will error, G is not undefined

G works only in its function body.

So b=function A (x) {...} Does not affect the global variable A,

3.

1     function A (x) {23         return x * 2; 4 5     }67     var  A; 8 9     // Popup function Body

There seems to be no suspense, the function declaration executes before any statement, and the seventh line simply re-declares a, but does not make any changes to a.

1     var fn = 1; 2     function fn () {3         alert ("FN"); 4     }5     alert (FN);   1

If the FN is re-assigned, it will change the FN, the function declaration and function expression of the contents can refer to Uncle Tom's detailed explanation (http://www.cnblogs.com/TomXu/archive/2011/12/29/2290308.html)

4.

1             function B (x,y,a) {2                 arguments[2]=10; 3                  45                         //

In fact, in the function body, a and arguments[2] are references to the same parameter, as follows:

1     function fn (v) {2         alert (arguments[0]===3    }4     //  True

However, if you manually modify V or arguments in the function body when the passed parameter value is empty, it will result in no longer a reference to the same object

1             functionfn (v) {2                 //do not make any changes to V and arguments3Alert (v = = = Arguments[0]);//true4                 5                 6v = 10;7Alert (v);//Ten8Alert (arguments[0]);//undefined9alert (ARGUMENTS[0]===V);//falseTen                  One                 /* A arguments[0]=10; - alert (arguments[0]);//10 - alert (v);//undefined the alert (arguments[0]===v);//false*/ -             } -FN ();

5.

1     function A () {23         alert (this); 4 5     }67     a.call (null);

The syntax for call in JavaScript is call (Thisobj,arg1,..., argn)
Parameter thisobj: An option that will be used as the object of the current object.
Parameter arg1,..., argn: Optional, the method parameter sequence is passed.

If no thisobj is empty, the call is made by default with global (window):

1             functionfn () {2Alert This);3             }4Fn.call (NULL);//[Object window]5Fn.call ();//[Object window]6Fn.call (undefined);//[Object window]7Fn.call (window);//[Object window]

You think you know a lot about javascript? (Personal answer)