beforeunloadThe beforeunload event is fired when the current window is about to be unloaded. Typically this is used to display a dialog to confirm if users really want to leave the page when there is unsaved data that would be lost.limitedhttps://html.spec.whatwg.org/multipage/nav-history-apis.html#the-beforeunloadevent-interfacehttps://developer.mozilla.org/docs/Web/API/BeforeUnloadEventapi.BeforeUnloadEventapi.BeforeUnloadEvent.user_interactionapi.Window.beforeunload_eventapi.Window.beforeunload_event.preventdefault_activationhttps://nowyoucanuse.com/features--beforeunload.html