title: Multiple OnBeforeUnload
body: <p>I am writing a JS which is used as a plugin. The JS has an onbeforeunload event.</p>
  
  <p>I want suggestions so that my onbeforeunload event doesn't override the existing onbeforeunload event (if any). Can I append my onbeforeunload to the existing one?</p>
  
  <p>Thanks. </p>