I am attempting this same thing but when I use the code:
|var ddl = $find("<%= rcbRegion.ClientID %>");
I get the following error:
The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).
Per the advice of another site, I changed the <%= to <%#. The page does load but, the call to $find returns null.
I am attempting to base the values of one combo box off the selection of another. Following your examples, I am attempting to get a handle to the combo box and call "requestItems(sender.get_text(),false);" I have altered the ItemRequested event of the combo to use the text but I cannot seem to get a handle to the combo box client side. Any help or alternative solution is appreciated.