javascript - onChange event not working when change automated -

i have onchange event on 1 select box (usagedisplays), populates next select box based on selected value of first:

<html:select name="usagedisplays" property="name" indexed="true" onchange='<%="populateyearslist(" + id + "," + name + ")"%>' /> 

this works fine when user selects value in usagedisplays, doesn't work @ when value of usagedisplays set based on radio button choice earlier on page

getelementbyname("usagedisplay.name").value = username; 

hi onchange fire when select value must change on page load not select first , change

programmatically changing value doesn't fire change event, occurs if user focuses element, changes value , puts focus elsewhere.

options manually call onchange listener, dispatch change event on element, or manually bubble change event going dom looking parents onchange listener , calling them.

here answer seems fit bill: trigger onchange event manually

some links:

mdn dispatchevent (standards compliant): https://developer.mozilla.org/en/dom/element.dispatchevent msdn fireevent (ie proprietary): http://msdn.microsoft.com/en-us/library/ie/ms536423(v=vs.85).aspx