@Aaviii 

try this

  var arr = new global.ArrayUtil();
    var currArr = current.watch_list.toString().split(',');
    var prevArr = previous.watch_list.toString().split(',');
    var gm = arr.diff(currArr, prevArr);
    gs.info("Test" + gm);

If my response helped please mark it correct and close the thread so that it benefits future readers.