[popup] Consider to add popupshowing, popupshown, popuphiding and popuphidden events

[smaug----]

The proposed popup elements shares lots of common with XUL popup element (which is used in Firefox UI to create all sorts of popups). Very common way to use a popup is to fill its content just when it is about to be shown. That is why there is popupshowing DOM event. Other commonly used events are popupshown, popuphiding and popuphidden.

(There is also popuppositioned event.)

[gregwhitworth]

This was discussed in this week's meeting with the following resolution:

RESOLUTION: Events should be emitted when show or hide state changes (i.e. beforeShow, show, beforeHide, hide). Event timing and names to be defined.

Minutes are here

[github-actions]

There hasn't been any discussion on this issue for a while, so we're marking it as stale. If you choose to kick off the discussion again, we'll remove the 'stale' label.

[mfreed7]

The pop-up API has evolved significantly since this question was raised. In particular, the show and hide events have been more fleshed out as synchronous events, which allows a pop-up to have its content updated prior to being shown, and/or retrieve data from the pop-up prior to being hidden. Also, the animation behavior has been resolved, allowing easy animations of pop-up show and hide. I'm curious what use cases are still left out of the existing proposal that might require more events than just show and hide. Thoughts?

[mfreed7]

I'm inclined to close this issue, given that I believe (subject to being told I'm wrong!) that the current proposal functionality covers all relevant use cases.