docs: function(callback, thisArg) {
        if (Array.prototype.map) {
          return arr.map(callback, thisArg);
        } else {
          var len = arr.length >>> 0,
              A = new Array(len),
              i = 0;
          for (; i < len; i++) {
             A[i] = callback.call(thisArg, arr[i], i, arr);
          }
          return A;
        }
      }