Detecting browsers that don't support onunload/onbeforeunload

Question

Of all the browsers, it seems that only Opera doesn't support onunload/onbeforeunload events. (It's been fifteen years now, Opera!) Solutions for this issue have been covered many times, here for example: onbeforeunload support detection

Unfortunately, as of Opera 11.51, ("onbeforeunload" in window) == true, but the actual onbeforeunload event is never executed!

My web application needs to send data to server when a user leaves the page; I'm using a synchronous ajax request for this. It looks like I have to resort to using a "Save" button somewhere on the page to cover up for Opera issues. However, I don't want this button to confuse users whose browsers are capable of auto-saving through ajax, so I'd really like the button to only show up in Opera.

Is my only choice browser-detection? The problem is, Opera has an option to disguise itself as other browsers anyway.

Answer 1

I can't reproduce your finding that 'onbeforeunload' in window is true in Opera 11.5x. This is the best way to do it and should still work. Are you sure you haven't left in some definition somewhere, e.g. you've written

onbeforeunload = function (){ ... }

later in the same script that does the feature detection? If you do alert(window.onbeforeunload), what do you see? Could you share a link to the page with the problem?