Notify user page was modified if trying to exit, what's the technique?
<p>If a user is on a page with a form, and they have edited something, and then try and navigate to another page, how can I notify them?</p>

<p>How do people do this?</p>

<p>Is it a matter of computing a hash of all the input fields and comparing if they are exiting the page? </p>

<p>Is there a on page unload event?</p>
