Serious unload approach for web application

I know there is a lot of questions already answered related to this.

People developing serius web applications need a robust way to avoid data-lost when the page is unloaded.

By now 'beforeunload' control is poor and dangerous, IMHO, specially because you can't offer a custom dialog and also the 'Don't show this message again' that disable the unload detection....

I'd like ( I need, we need) a way to ask the user for 'Do you want to be conveniently warned allways when close the browser tab, or refresh the page, to avoid data lost ?

Or something like "This app wants to warn you allways when the page is going to be closed, Do you let it to have this behaviour" . (as when you install an app at your smartphone'

Have we do it with extensions ? I dont want.... Neither to change from html5/js to app or web app... I want to use pure Js/html5....

Does anybody knows what are doing for this google, mozilla, MS, Apple, etc ?

Any ideas would be appreciated.