关于选择排序，将一组数，从小到大选择排序

     var arr = [5, 4, 3, 2, 1];
        for (var j = 0; j < arr.length - 1; j++) {
            for (var i = j + 1; i < arr.length; i++) {
                if (arr[i] < arr[j]){
                    var tmp;
                    tmp = arr[i];
                    arr[i] = arr[j];
                    arr[j] = arr[i];
                    arr[i] = tmp;
                }
            }
        }
        console.log(arr);