Input Box "Onchange" event

Hi,
>
I've got an input box with popup calendar (date picker) all generated
using javascipt.
>
Once a date is selected from the datepicker window, the date value is
populated back to the input box.
>
The problem is that the input box onchange event does not kick off. The
onchange event only kicks off when value is manually entered. I know
there is no "On Value Change" event for input box. Is there any way to
kick off a function when the value in the input box is changed via
javascipt ?
>
Any help is much appreciated. Thanks in advance.