How do I know that a form input has changed?

Question

I have a form generated by <% Ajax.BeginForm() {} %> which contains a lot of inputs and texareas.

When an input value change, I need to know about it

Answer 1

I would do this with jQuery. It would be something like this (just a draft, you may need to add/change some code):

$(document).ready(function() {  
    $('#formId:input').each(function(key) {
        $(this).change(function() {
            $(this).addClass('dirty');
        });
    });
});

Then, before POSTing, check if there is a dirty input. You can even add some color by using the dirty css class.

EDIT: typo fixed 'changed' to 'change'