Copy pageCopy pageCopy this page as Markdown for LLMsView as MarkdownView this page as plain textOpen in ClaudeAsk questions about this pageOpen in ChatGPTAsk questions about this pageOn this pageBeforeUnloadEvent-1BeforeUnloadEvent: {(): BeforeUnloadEvent; prototype: BeforeUnloadEvent;}; Type Declaration Returns BeforeUnloadEvent prototype prototype: BeforeUnloadEvent;