求一个数组中的最大值。定义成函数

function getMax(arr) {
            var max = arr[0];
            for (var i = 0; i < arr.length; i++) {
                if (arr[i] > max) {
                    max = arr[i];
                }
            }
            return max;
        }
        var arr1 = new Array();
        arr1[0] = 20;
        arr1[1] = 10;
        arr1[2] = 21;
        alert (getMax(arr1));