Create javascript popup when visitor leaves page

We'd like a javascript popup that loads when the user leaves our checkout page. Is it possible for it to load an image with a "okay" or "leave" button? So if the user clicks out, leaves the page, clicks backspace, closes tab whatever, anything other then going ahead with the checkout it will popup this image in the center of the screen and you HAVE to click "yes or no" But instead of the usual console yes/no box we want it to display the image with the option of staying or leaving Thanks!