pop on page close?

Question

in an effort to reduce shopping cart abandonment, I would like to do a pop window offering a 5% coupon code when a user goes to close the shopping cart page.

I've seen these, and yes they can be annoying, but I can't seem to locate code for doing this.

Answer 1

There is a window event called onbeforeunload. You can return a string in that event and it will echo that string to the user and prevent the window from closing. So you can do something like:

window.onbeforeunload = function( ) {
    return 'Are you sure you want to close this window?';
}

Answer 2

after 

window.close()

you trying to open a new

window.open()