How to fire select value change even in a combo box programmatically?

I've a combo box and want to select an option value. I'm using something like:

$("#comState_city option:eq(0)").attr("value",chk[i]);
$("#comSt开发者_C百科ate_city option:eq(0)").attr("selected","selected");

But this isn't firing value change event. I want the onchange handler be called when I changed the value of a select element.

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$('#comState_city option:eq(0)').trigger('change');

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Try this one:

$("#comState_city").change(function(){
    alert($(this[this.selectedIndex]).val());
});