map兼容ie

// Production steps of ECMA-262, Edition 5, 15.4.4.19
// Reference: http://es5.github.com/#x15.4.4.19
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");
}

// 1. Let O be the result of calling ToObject passing the |this| value as the argument.
var O = Object(this);

// 2. Let lenValue be the result of calling the Get internal method of O with the argument "length".
// 3. Let len be ToUint32(lenValue).
var len = O.length >>> 0;

// 4. If IsCallable(callback) is false, throw a TypeError exception.
// See: http://es5.github.com/#x9.11
if (typeof callback !== "function") {
throw new TypeError(callback + " is not a function");
}

// 5. If thisArg was supplied, let T be thisArg; else let T be undefined.
if (thisArg) {
T = thisArg;
}

// 6. Let A be a new array created as if by the expression new Array(len) where Array is
// the standard built-in constructor with that name and len is the value of len.
A = new Array(len);

// 7. Let k be 0
k = 0;

// 8. Repeat, while k < len
while(k < len) {

var kValue, mappedValue;

// a. Let Pk be ToString(k).
// This is implicit for LHS operands of the in operator
// b. Let kPresent be the result of calling the HasProperty internal method of O with argument Pk.
// This step can be combined with c
// c. If kPresent is true, then
if (k in O) {

// i. Let kValue be the result of calling the Get internal method of O with argument Pk.
kValue = O[ k ];

// ii. Let mappedValue be the result of calling the Call internal method of callback
// with T as the this value and argument list containing kValue, k, and O.
mappedValue = callback.call(T, kValue, k, O);

// iii. Call the DefineOwnProperty internal method of A with arguments
// Pk, Property Descriptor {Value: mappedValue, : true, Enumerable: true, Configurable: true},
// and false.

// In browsers that support Object.defineProperty, use the following:
// Object.defineProperty(A, Pk, { value: mappedValue, writable: true, enumerable: true, configurable: true });

// For best browser support, use the following:
A[ k ] = mappedValue;
}
// d. Increase k by 1.
k++;
}

// 9. return A
return A;
};
}