mapping with map js javascript

_map.js

console.time('mapping in js');
var isAType = {};
isAType._array = "[object Array]";
isAType._function = "[object Function]";
isAType._string = "[object String]";

isAType.isFunction = function(fn) {
    return Object.prototype.toString.call(fn) === this._function;
}

isAType.isArray = function(arr){
    return Object.prototype.toString.call(arr) === this._array;
}

isAType.isString = function(arg){
    return Object.prototype.toString.call(arg) === this._string;
}

var _map = function (callBack,optionalThis){

    //by now assuming this is the Array
    if (isAType.isArray(this)){
        var mapped = [];
        var originalArray = this;
    }
    else if (isAType.isString(this)){
        var mapped = [];
        var originalArray = this.split('');
    }else
        return {'error':void(0)};

        var howManyArgs = arguments.length;
        if (_map.length === howManyArgs){
            console.log("we have all the args");
        }
        if ( isAType.isFunction( callBack) ){
            if (optionalThis){
            callBack.call( optionalThis , originalArray[i], i, originalArray);
            }
            for (var i = 0 ; i<originalArray.length; i++){
            mapped[i] = callBack.call(originalArray,originalArray[i], i, originalArray);
            }
            return mapped;
        }

};

    Array.prototype._map = _map;

    //real map function

    function _assert(what,describe){
        if (what){
        console.log("%c"+describe + "is true",'color:green');
        }
        else{
        console.log("c%"+describe + "is false",'color:red');
        }
    };

var _r1 = ['1','2','3'].map(Number);
_assert( isAType.isArray(_r1)&&_r1.length===3&&Number.isFinite(_r1[0]) , "Real map is mapping! " )

//fake _map function
var _f1 = ["1","2","3"]._map(Number);
_assert( isAType.isArray(_f1)&&_f1.length===3&&Number.isFinite(_f1[2]) , "f@ke map is m@pping! ;) " )

//real map function
var _r2 = ['1','2','3'].map(function(x){return Math.pow(x,2);});
_assert( isAType.isArray(_r2)&&_r2.length===3&&Number.isFinite(_r2[0]) , "Real map is mapping! again " )
//fake _map function
var _f2 = ['1','2','3']._map(function(x){return Math.pow(x,2);});
_assert( isAType.isArray(_f2)&&_f2.length===3&&Number.isFinite( _f2[1]), "fake m@p is mapping! again " )


//mozilla developer network  example
var kvArray = [{key:1, value:10}, {key:2, value:20}, {key:3, value: 30}];

var myCallBack = function(obj){
var rObj = {};
rObj[obj.key] = obj.value;
return rObj;
};

var reformattedArray = kvArray.map(myCallBack);
_assert( isAType.isArray(reformattedArray)&&reformattedArray.length===3&&typeof reformattedArray[0] === "object"  , "Real map is mapping! other one ");

var fakeformattedArray = kvArray._map(myCallBack);
_assert( isAType.isArray(fakeformattedArray)&&fakeformattedArray .length===3&&typeof fakeformattedArray [0] === "object"  , " Fake map is mapping! other one ;) ");

var str = '12345';
var rev = [].map.call(str, function(x) {
return x;
}).reverse().join('');

_assert(rev==='54321',"real map is reversing!")

var _rev = []._map.call(str, function(x) {
return x;
}).reverse().join('');

_assert(rev==='54321',"f@ke map is reversing!")

console.timeEnd('mapping in js');