@zensaiyuki This is exactly why I advise against using JavaScript's alert(), confirm(), or prompt() functions: They don't allow you to label your buttons anything other than "Okay" & "Cancel".
I generally prefer native UIs, but in this case: PLEASE implement your own! Preferably something non-blocking like GTK's InfoBars.
@alcinnz those also (at least in some browsers) block the main thread of execution.