Some questions about JS's clone () function __ function

Problem: Using JS to implement a clone () Cloning function, the function will input into the different types of values Number,string,undefined,boolean,function,null,object,array,regexp, Cloning a copy out of a, problem-solving code

Directly attached code,

function Clone (obj) {            var copy;             switch ( typeof obj) {                case ' undefined ': break;         & nbsp       case ' number:                 case ' string ':     & nbsp           case ' Boolean ':                 case ' function '
: copy = Obj;break;                 Case ' object ':               &N Bsp
    if (obj = null) copy = NULL;                     ELSE if (tostring.call (obj) = = ' [object Array] ') &NB Sp                                   & nbsp
      copy = [];       &NBSP
                for (var i in obj) Copy.push (Clone (Obj[i));                                   &     nbsp
else if (tostring.call (obj) = = ' [object RegExp] ')                     {
                        copy = obj;                                   & nbsp     else                      {      &NBS P
                copy = {};                          for (var j in obj)      
                      copy[j]= clone (Obj[j]); &nbSp                    {           }    
        return copy;
       }         var a=undefined;
        var b=1;
        var c= "Hello";
        var d=true;
        var add=function (a,b) {        return a+b;        }
        var e=null;
        var f=[1,2,3];
        var g=/^\s+/;         var h={        a:1,         b:2     &NBSP ;
 }         Console.log (typeof clone (a));
        Console.log (typeof clone (b));
        Console.log (typeof clone (c));
        Console.log (typeof clone (d));       &NBSP
Console.log (Clone (add) (1,2));
        Console.log (Object.prototype.toString.call (Clone (e)));
        Console.log (Object.prototype.toString.call (Clone (f)));
        Console.log (Object.prototype.toString.call (Clone (g)));          Console.log (Object.prototype.toString.call (Clone (h)));

Results:

second, the question

When I first saw this problem, I thought TypeOf [1,2,3] The result is, this can do, regular expression, Null,object typeof are all. Look at the code above, which is solved with Object.prototype.toString.call (obj) or tostring.call (obj).

So why not just use obj.tostring (). Let's take a look at what obj.tostring () will output.

Null and undefined actually went wrong, that's for sure, because ToString () is not capable of completing null and undefined transformations, using string () to

If string () is not converted to null or undefined, it is automatically converted to ToString (). It's far away. Let's get back to business.

So what's the result of using Object.prototype.toString.call (obj)?

Incredibly different, what's going on here.

It turns out that although types such as Array,null are instances of object, but each of them rewrites the ToString () method, we try to verify that:

var arr=[1,2,3];
Console.log (Array.prototype.hasOwnProperty ("tostring"))//Determine whether the prototype has a toString () method
Console.log (arr.tostring ()) ;
Delete array.prototype.tostring;//deletes the rewritten toString
console.log ("Array.prototype.hasOwnProperty" in the Array prototype) ToString "));
Console.log (Arr.tostring ());

Results:

It's obvious that it's been rewritten. third, there are some words

In fact, some people will say that you can use arr instanceof array to determine whether the array, in fact, instanceof in the frame object built in the case will be invalidated.