Beforeunload for PWA

Adam Eisenreich akxe at
Tue Mar 30 12:39:32 UTC 2021

I think that PWA should have the ability to override the default 
beforeunloadEvent message.

Since returning string is already deprecated and removed from all browsers, 
it would be safe to change how the returned value is handeled.

All proposed changes should only apply to installed PWAs!

If the return value is:

   1. HTMLFormElement - display the element in front of everything with a 
   backdrop disabling every other interaction. 
   * CSS of the page should apply to this element. 
   * Browser listens to the "submit" event of the form; based on the 
   truthiness of the return value from the form submit event either close 
   window or hide message while keeping window open
   * Closing the window via system buttons a second time (while dialog is 
   open) will force the closing of the page.
   2. String - Display the standard beforeunload dialog that used to have 
   the custom message.

What are your thoughts? Should PWA have the exception and have elevated 
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