js冒泡排序

//冒泡排序
var arNum = [13, 12, 4, 131, 57, 2, 59];
var a = 0;
for (var j = 0; j < arNum.length; j++) {
    for (var k = 0; k < arNum.length - j; k++) {
        if (arNum[k] > arNum[k + 1]) {
            a = arNum[k];
            arNum[k] = arNum[k + 1];
            arNum[k + 1] = a;
        }
    }
}
for (var i in arNum) {
    console.log(i)
    if (i != arNum.length - 1) {
        document.write(arNum[i] + ',');
    } else {
        document.write(arNum[i]);
    }
}