Shropshire, Andrew A wrote:
For those that don't, making the unload event cancellable won't break anything (it won't be fired multiple times because the first time it's fired is the last for the page because it gets unloaded on the first fire since these existing web apps don't know that it can be cancelled and thus don't do it).
That last part does not follow, though we all wish it did. There are plenty of cases of web apps and web pages doing cargo-cult copy-paste programming, with operations that are no-ops happening all over. If they suddenly stop being no-ops, these pages break. Some research into any web browser bug database would pull up a number of examples.
That is, I will bet money there are pages out there that _do_ try to cancel the unload event and that would break if it were actually canceled.
-Boris
