Check form for changes and only get the difference

form_check.js

function getFormOriginalState()
{
  startItems = convertSerializedArrayToHash($form.serializeArray());
}

function checkFormForChanges()
{
  var currentItems = convertSerializedArrayToHash($form.serializeArray());
  var dataToSubmit = hashDiff(startItems, currentItems);
  return dataToSubmit;
}

function hashDiff(hash1, hash2) {
  var diff = {};
  for (var k in hash2)
  {
    if (hash1[k] !== hash2[k])
    {
      diff[k] = hash2[k];
    }
  }
  return diff;
}

function convertSerializedArrayToHash(array) {
  var r = {};
  for (var i = 0; i<array.length; i++)
  {
    r[array[i].name] = array[i].value;
  }
  return r;
}

function getFormData()
{
  var data = checkFormForChanges();
  data.user_id = user.id;
  validateFormData(data);
}