I think you might be changing the hidden input's value with JavaScript, as its not possible otherwise.
So just after you change the value of the field, in the next line, execute the code which you want to execute onchange.
You are correct. I am changing value via scripts (note plural). I did not want to have to change every script that updates the value of the field. I wanted the field to detect the change and fire the event, the same as if the user had made the change.
I have an add/edit/delete screen. On it I have several methods for the user to fill the form elements i.e. they can type in the field, they can use one of my search methods which open sub-windows for lookup purposes where they can select a record which is then backfilled on the calling screen via script. I am now adding ajax communication which goes out to look for the next 30 records which can be used by the user for browsing. So as you see there are a number of ways to fill the field. But only the user input (typing in the field) will trigger the onChange. And of course on my previous search methods I use script to mark the change. I was just hoping for a single point to capture any change that occurred regardless of the method of change.
Is that possible?