I have a multi-step form and user can navigate to any page to modify or add information. There is a menu that shows the current progress, the steps the user has completed, and allows to navigate to any completed or pending step.

In spite of a big button Save and Continue some users click this menu to navigate further. I have to check - if values have changed in a form and ask: Save changes? Yes/No.

What is the best way (with minimum client-side JavaScript code) you suggest me to check if form values have changed?

Edited a bit later:

I forgot to tell that the multi-step form uses postback between steps.