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unload

The unload event is fired when the document or a child resource is being unloaded.

It is fired after:

beforeunload (cancellable event)
pagehide

The document is in a particular state:

All the resources still exist (img, iframe etc.)
Nothing is visible anymore to the end user
UI interactions are ineffective (window.open, alert, confirm, etc.)
An error won't stop the unloading workflow

Please note that the unload event also follows the document tree: parent frame unload will happen before child frame unload (see example below).

Bubbles	No
Cancellable	No
Target objects	defaultView, Document, Element
Interface	`UIEvent` if generated from a user interface, `Event`
Default action	None

Properties

Property	Type	Description
`target` Read only	`EventTarget`	The event target (the topmost target in the DOM tree).
`type` Read only	`DOMString`	The type of event.
`bubbles` Read only	`Boolean`	Whether the event normally bubbles or not.
`cancelable` Read only	`Boolean`	Whether the event is cancellable or not.
`view` Read only	`WindowProxy`	`document.defaultView` (`window` of the document)
`detail` Read only	`long` (`float`)	0.

Example

<!DOCTYPE html>
<html>
  <head>
    <title>Parent Frame</title>
    <script>
      window.addEventListener('beforeunload', function(event) {
        console.log('I am the 1st one.');
      });
      window.addEventListener('unload', function(event) {
        console.log('I am the 3rd one.');
      });
    </script>
  </head>
  <body>
    <iframe src="child-frame.html"></iframe>
  </body>
</html>

Below, the content of child-frame.html:

<!DOCTYPE html>
<html>
  <head>
    <title>Child Frame</title>
    <script>
      window.addEventListener('beforeunload', function(event) {
        console.log('I am the 2nd one.');
      });
      window.addEventListener('unload', function(event) {
        console.log('I am the 4th and last one…');
      });
    </script>
  </head>
  <body>
      ☻
  </body>
</html>

When the parent frame is unloaded, events will be fired in the order described by console.log messages.

Specifications

Specification	Status	Comment
UI Events The definition of 'unload' in that specification.	Working Draft

Related Events

Specifications

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https://developer.mozilla.org/en-US/docs/Web/Events/unload