```
            if(!$('fieldset.quote-step4').hasClass('show')) {
                window.onbeforeunload = function() {
                    return "Are you sure you want to leave the quote request page? This will reset the form.";
                }
            } else {
                window.onbeforeunload = undefined;
            }

```

I have the above in a script inside of a private function that's causing a "not implemented" error in ie8.

The specific line that causes the error is: `window.onbeforeunload = undefined;`

From what I've read in other questions `window` should be declared as a local variable to fix this issue-- but I'm not sure how.

Can anyone explain this bug to me and a possible solution? 

Thank you!