I have an HTML form with over 20 fields. I also have a couple of links on the page which will lead the user away from the form... potentially without having saved any changes.

I want to warn (JS confirm) the user onClick of these links if any of the form fields have changed, but I don't want to create a huge switch statement that I then need to maintain as I add new fields to the form. I know how to create a long list of 'if' statements in Javascript, naming each of the fields and checking each value, but I don't want to do that if I can get away with it.

What's the easiest way to check if the user has changed at least one of the field values?