onunload event is used to trigger an action once a
web page has unloaded (or the browser window has been closed)—effectively,
the point at which the visitor to that page has navigated away by
following a link, submitting a form, or using some other mechanism that
causes a new page to be loaded in its place.
It may also be used in
the context of
framesets to indicate that the child
frame elements have unloaded or been replaced with new
When used as an inline attribute,
onunload is most frequently applied to the
body element, as shown below:
This attribute has no fixed value.
It’s up to the author to decide on the scripting that’s included here, be
that a call to one or more defined functions, or a simple
Every browser listed supports this attribute. However, inline event handlers such as this should be avoided. In the same way that inline CSS styles are frowned upon but externally defined CSS styles are considered good practice, inline event handlers should be stripped out and replaced with events attached unobtrusively through the DOM.