I would like to give some feedback about ...

Your result: "hello" Right result: "" Fail: commonWords(["one,two,three","four,five,six"])

My result is "hello"?! In my browser this code works correct. It returns empty string. Right?

"use strict"

var arrayEmpty = [];

function commonWords(string1, string2) {
    var arrayString1 = string1.split(',');
    var arrayString2 = string2.split(',');


    for (var i = 0; i < arrayString1.length; i++) {
        for (var n = 0; n < arrayString2.length; n++) {
            if (arrayString1[i] === arrayString2[n]) {
                arrayEmpty.push(arrayString1[i]);
            }
        }
    }


    for (var j = 0; j < arrayEmpty.length; j++) {
        for (var k = 0; k < arrayEmpty.length; k++) {
            if (arrayEmpty[k] > arrayEmpty[k+1]) {
                var temp = arrayEmpty[k];
                arrayEmpty[k] = arrayEmpty[k+1];
                arrayEmpty[k+1] = temp;

            }    
        }
    }


    if (arrayEmpty[0] == undefined) {

        return arrayEmpty.join();
    }



    return arrayEmpty.join(',');
}

From: https://js.checkio.org/mission/common-words/solve/

HTTP_USER_AGENT:

Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36