Intercept a4j:commandButton request

I am developing web application using A4J, Richfaces. One of my requirement is, I need to check if the user has changed any values in the form when he is trying navigate away from the page. I have save and cancel buttons in the page. I am using `a4j:command` button for cancel functionality. Clicking on cancel button should do below things - Check if the user has modified anything in the form (this I am doing by using javascript and have a flag if user changed any values) - Display confirmation box (javascript confirm with values "Do you really want to discard the changes -- YES NO") when user changes form values - If user says YES, then submit the form using AJAX (by using A4J) My a4j command button code is like this ``` <a4j:commandButton action="MyClass.cancel_action" onclick="checkIsPageChanged()"/> ``` The issue here is, while using using `a4j:commandButton`, I cannot call the intermediate javascript function (the function which checks if user has updated any values and displays confirmation box) and then submit the request using ajax. I have looked at the code generated by JSF and the code is like (not the exact but syntact) ``` <input type="button" onclick="checkIsPageChanged();AJAX.submit('')/> ``` The thing is when I click on button, it is calling only `checkIsPageChanged()` and not calling `AJAX.submit()`. Any workaround for this will help me. Thank you in advance.