Generic way to detect if html form is edited

I am not sure if I get your question right, but what about addEventListener? If you don't care too much about IE8 support this should be fine. The following code is working for me:

var form = document.getElementById("myForm");

form.addEventListener("input", function () {
    console.log("Form has changed!");
});

In pure javascript, this would not be an easy task, but jQuery makes it very easy to do:

$("#myform :input").change(function() {
   $("#myform").data("changed",true);
});

Then before saving, you can check if it was changed:

if ($("#myform").data("changed")) {
   // submit the form
}

In the example above, the form has an id equal to "myform".

If you need this in many forms, you can easily turn it into a plugin:

$.fn.extend({
 trackChanges: function() {
   $(":input",this).change(function() {
      $(this.form).data("changed", true);
   });
 }
 ,
 isChanged: function() { 
   return this.data("changed"); 
 }
});

Then you can simply say:

$("#myform").trackChanges();

and check if a form has changed:

if ($("#myform").isChanged()) {
   // ...
}