I'm working on a fix for an old site I didn't write, and my solution
for this problem should be simple.

Among about 12 dropdown lists, one of them has to be loaded with 30k+
items which causes slowdown during site-load on some weaker computers.
I want to add an OnClick event to the dropdown to populate itself when
the user selects it.

I figure this would be something like creating a javascript function
to call a VB.NET code-behind function with the ID of the selected
dropdown. I'd like to add this function to only the one dropdown
(which is generated dynamically in code-behind) when the condition for
"not loading the data into the control" is met, this way only that
dropdown will make the callback and would only populate the one
dropdown.

I'm very new to AJAX and any help at all would be appreciated. I will
respond with a solution if I find one.

Thank you in advance!