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;
  };      
}