[MDN schreibt](https://developer.mozilla.org/de/docs/Web/API/WindowEventHandlers/onbeforeunload): > Since 25 May 2011, the HTML5 specification states that calls to window.alert(), window.confirm(), and window.prompt() methods may be ignored during this event. See the HTML5 specification for more details. _Rolf_

MDN schreibt: > Since 25 May 2011, the HTML5 specification states that calls to window.alert(), window.confirm(), and window.prompt() methods may be ignored during this event. See the HTML5 specification for more details. _Rolf_