Join MDN and developers like you at Mozilla's View Source conference, 12-14 September in Berlin, Germany. Learn more at https://viewsourceconf.org

BeforeUnloadEvent

この記事はまだボランティアによって 日本語 に翻訳されていません。ぜひ MDN に参加して翻訳を手伝ってください!

The beforeunload event is fired when the window, the document and its resources are about to be unloaded.

When a non-empty string is assigned to the returnValue Event property, a dialog box appears, asking the users for confirmation to leave the page (see example below). When no value is provided, the event is processed silently.

Bubbles No
Cancelable Yes
Target objects defaultView
Interface Event

Examples

window.addEventListener("beforeunload", function( event ) {
  event.returnValue = "\o/";
});

//is equivalent to
window.addEventListener("beforeunload", function( event ) {
  event.preventDefault();
});

Webkit-based browsers don't follow the spec for the dialog box. An almost cross-browser working example would be close to the below example.

window.addEventListener("beforeunload", function (e) {
  var confirmationMessage = "\o/";

  (e || window.event).returnValue = confirmationMessage;     //Gecko + IE
  return confirmationMessage;                                //Webkit, Safari, Chrome etc.
});

See also

ドキュメントのタグと貢献者

 このページの貢献者: fscholz, kscarfone, rabimba
 最終更新者: fscholz,