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var arr1 = [1,2,3,4,5];
alert(arr1.map(
	function(element) {
		return element * 2;
	}
)); // 输出：[2,4,6,8,10]

function MyArray(arr) {
	this.arr = arr;
}
MyArray.prototype.map = function(func) {
	var newArr = [];
	for (var i = 0; i < this.arr.length; i++)
		newArr[i] = func(this.arr[i]);
	return newArr;
};
var arr2 = new MyArray([1, 2, 3, 4, 5]);
alert(arr2.map(
    function(element) {
        return element * 2;
    }
)); // 输出：[2,4,6,8,10]