onbeforeunload Event

Example

Call a function when the page is about to be unloaded:

Description

The onbeforeunload event occurs when a document is about to be unloaded.

This event allows you to display a message in a confirmation dialog box to inform the user whether he/she wants to stay or leave the current page.

The default message that appears in the confirmation box, is different in different browsers. However, the standard message is something like "Are you sure you want to leave this page?".

This message cannot be removed, unless you call preventDefault() on the event.

Syntax

In HTML:

<element onbeforeunload="myScript">

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In JavaScript:

object.onbeforeunload = function(){myScript};

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In JavaScript, using the addEventListener() method:

object.addEventListener("beforeunload", myScript);

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Technical Details

Bubbles:	No
Cancelable:	Yes
Event type:	UiEvent if generated from a user interface, Event otherwise
HTML tags:	<body>
DOM Version:	Level 2 Events

Browser Support

onbeforeunload is a DOM Level 2 (2001) feature.

It is fully supported in all browsers:


Chrome	Edge	Firefox	Safari	Opera	IE
Yes	Yes	Yes	Yes	Yes	9-11

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