$('#multiselect1').on('change', function(){
var selected = $(this).find("option:selected");
var arrSelected = [];
// selected.each(function(){
// arrSelected.push($(this).val());
// });
// The problem with the above selected.each statement is that
// there is no iteration value.
// $(this).val() is all selected items, not an iterative item value.
// With each iteration the selected items will be appended to
// arrSelected like so
//
// arrSelected [0]['item0','item1','item2']
// arrSelected [1]['item0','item1','item2']
// You need to get the iteration value.
//
selected.each((idx, val) => {
arrSelected.push(val.value);
});
// arrSelected [0]['item0']
// arrSelected [1]['item1']
// arrSelected [2]['item2']
});