Js fails to load in IE 7 on combobox

Js fails to load in IE 7 on combobox

I have some combo boxes that work perfectly on every browser except IE7
the code is :
$('.custom-select select').change(function () {
var str = "";
$(this).find('option:selected').each(function () {
str += $(this).text() + " ";
});
$(this).siblings('.option-ch').text(str).trigger;
}).trigger('change');
this triggers the action of my combo box action that dosent work on IE 7
can someone help me with this please?
If I chose an option from the options in the combo list they dont remain
in the combo box as selected.