JS string combination

  Note that the data types should be consistent

    // add to 
    function strAdd(str1, str2){
        if(str1 == null || str1 == '')
        return str2;
        if(str2 == null || str2 =='')
        return str1;
        var ary = str1.split(",");
        ary.push(str2);
        return ary.join(",");
    }

    //  Delete 
    function strDel(str1, str2){
        if(str1 == null || str1 == '')
        return "";
        if(str2 == null || str2 == '')
        return str1;
        var ary = str1.split(",");
        var index = ary.indexOf(str2);
        if (index > -1) {
            ary.splice(index, 1);
        }
        return ary.join(",");
    }