Here are some (all?) ScriptUI events we have discovered so far:
Event Type (string) Handler Alias (if any) Target Widget(s) — onDraw any [not an ‘actual’ event though, see documentation on DrawState object.] move onMove Window moving onMoving Window resize onResize Window resizing onResizing Window show onShow Window close onClose Window focus onActivate (Window only) various (Window, EditText, Button…) blur onDeactivate (Window only) various (Window, EditText, Button…) change onChange various (EditText, Slider, Scrollbar, ListBox…) changing onChanging EditText, Scrollbar, Slider click onClick Button, IconButton, Checkbox, RadioButton (maybe others) — onDoubleClick ListBox mousedown — any mouseup — any mousemove — any mouseover — any mouseout — any enterKey onEnterKey EditText keyup — EditText (maybe others) keydown — EditText (maybe others) — onShortcutKey (Windows OS only) Window — onCollapse TreeView — onExpand TreeView — onSelect (?) (Need more detail on this one…) — onDisplay (?) (Need more detail on this one…)
Note 1. — Event types (strings) involve addEventListener and then an actual event handler of your own that will (assumedly) behave as detailed in ECMA DOM Level-3 events, despite pitfalls and cross-platform issues. By contrast, the onXYZ aliases only partially capture the underlying events and shouldn't be considered equivalent to pure event handlers. There are many things you can only do using event listeners.
Note 2. — Many great examples and additional info are exposed in ScriptUI For Dummies by Peter Kahrel: ScriptUI for dummies | Peter Kahrel
In the Photoshop environment you can respond to clicks on dropdown lists, but apparently not in InDesign. Earlier today I found that I can work around the lack (in InDesign) of a click response for the dropdown, simply by putting a click response on the group that includes the dropdown - but the user does have to click next to the dropdown, not directly on top of it. And just now, writing this response, I tried change with the dropdown and it did activate the event handler, as I added under (2) above. So that's my solution after I rewrite my complex window specification -- lots more typing but it gives the user a better experience!
So I guess I have to continue reworking the dialog specification so I can include some click responses... Tedious!
I think your answer is not complete (as if there is such out there!), but I'll give you credit for a correct answer.