How to trap the URL of the page to which the user is navigating off from current page

I want that whenever a user tries to navigate away from my page, I be able to trap the destination URL. Whenever someone would want to navigate away, the window.onunload will fire up. But how to trap the target URL? Any suggestions?

Do not think you have any control on figuring that out. Sort of a privacy issue unless it is a link on your page and you can add onclick handlers on them.

Eric