在网页上触发组合框的 OnChange

Question

I am working on an application that can fill out a form automatically. The issue I am having is that there are two comboboxes on the webpage.
Combobox1 has items that change depending on what is selected in Combobox2.
Combobox2 has items.
Combobox2 has the following code:

onchange="javascript:setTimeout('__doPostBack(\'ctbnss_2103\',\'\')', 0)"

If I were to manually select an item in Combobox2, a loading gif pops up on the page, and once finished, Combobox1 has new items. This is the desired result.

If I select an item in Combobox2 through code, no loading gif pops up, and Combobox1 still has the old items even though a Combobox2 item has been successfully selected. This is my code:

eoBrowserWV.EvalScript("frames['main'].document.getElementById('combobox2').value='" + stringItem1 + "';");

How do I adjust this code so that Combobox1 refreshes? I know that I have to somehow trigger the onchange event after changing Combobox2, but while I am successful in changing Combobox2, I am not sure what code I have to add after the above code, to fire OnChange.

I tried the below, without success, as it appears that .trigger is not a function:

wvMain.EvalScript("frames['main'].document.getElementById('combobox2').trigger('change');");

And I have also tried this, without success, due to this error: Uncaught TypeError: Failed to execute 'dispatchEvent' on 'EventTarget': parameter 1 is not of type 'Event'.'

wvMain.EvalScript("frames['main'].document.getElementById('combobox2').dispatchEvent('change');");

Answer 1

解决了它：

wvMain.EvalScript("frames['main'].document.getElementById('combobox2').dispatchEvent(new Event('change'));");