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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. });