Fill Combo on change Trigger using JQuery

I have two DropDowns, on change event of one Drop Down, i haved filled the 2nd Drop Down. when i trigger the change event of first drop down on Arrow Keys, its not working, while on Mouse click its working fine. Here is my Code..

$('#cmbCategory').on('change', function () {
    //alert($(this).val());
    // the below function will get Sub Categories from DataBase.
    getSubCategories($('#cmbCategory :selected').val(), '');
}).keydown(function (e) {
    if (e.which == 37 || e.keyCode == 38 || e.keyCode == 39 || e.keyCode == 40) {
        $(this).trigger('change');
    }
});

This code works fine while using Mouse, but doesn't work on Arrow Keys. Any Help..

I think you have to add keyup event or you can also use keypress event

$("#cmbCategory").keyup(function(e) 
{
        if (e.keyCode == 40) 
        {  
            getSubCategories($('#cmbCategory :selected').val(), '');
        }
        if(e.keyCode==38)
        {
            getSubCategories($('#cmbCategory :selected').val(), '');
        }

});

Note: Above code is not tested