There is nothing more irritating than when you are typing out a long message in a text box and you accidentally move backwards, or clicking on a link and moving off page, therefore losing data you may have entered. There is a solution to stop this happening and it involves the onbeforeunload event.
Although not technically a fully supported event, onbeforeunload is run just before the page is unloaded out of cache. The onunload event occurs right after this, and it is too late by that point.
To prevent a user from moving out of the current page without some form of warning you will need to return some text with the onbeforeunload event. In some browsers that text will be used as part of the message, some browsers will ignore the message but continue anyway.
Include the following body tag in the page you want to incorporate this feature into.