The onunload event occurs once a page has unloaded (or the browser window has been closed).
onunload occurs when the user navigates away from the page (by clicking on a link, submitting a form, closing the browser window, etc.)
Note: you will also trigger the unload event when a user relaods the page (and the onload event).
The onunload event is supported in IE, Firefox, and Safari, but not supported properly in Chrome or Opera.
Your message has been sent to W3Schools.