ie8不支持javascriptmap方法

if (!Array.prototype.map) {
 Array.prototype.map = function(callback, thisArg) {

 var T, A, k;

 if (this == null) {
 throw new TypeError(" this is null or not defined");
 }
 var O = Object(this);
 var len = O.length >>> 0;
 if (Object.prototype.toString.call(callback) != "[object Function]") {
 throw new TypeError(callback + " is not a function");
 }
 if (thisArg) {
 T = thisArg;
 }
 A = new Array(len);
 k = 0;
 while(k < len) {
 var kValue, mappedValue;
 if (k in O) {
 kValue = O[ k ];
 mappedValue = callback.call(T, kValue, k, O);
 A[ k ] = mappedValue;
 }
 k++;
 }
 return A;
 }; 
}