Window: unload event

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

Bubbles No
Cancelable No
Interface Event
Event handler property onunload

It is fired after:

The document is in the following 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).

The unload event (and onunload event handler) are not the right features to use with sendBeacon. Instead for sendBeacon, use the visibilitychange and pagehide events. See discussion in the comments for the blog post Beacon API is broken.

Examples

<!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 the console.log() messages.

Specifications

Specification Status Comment
HTML Living Standard
The definition of 'unload' in that specification.
Living Standard

Browser compatibility

BCD tables only load in the browser

See also