Ember serializer fn to save only dirty properties

gistfile1.coffee

// original thread: http://discuss.emberjs.com/t/dirt-tracking-with-ember-data-only-save-dirty-properties/4191/22  
// made by Glavin001

serializeAttribute: function(snapshot, json, key, attributes) {
// Check if new record
if (snapshot.get('isNew'))  {
  // Is new
  return this._super(snapshot, json, key, attributes);
}  else {
  // Check if current attribute is in flight
  let attrKey = '_internalModel._inFlightAttributes.'+key;
  if (snapshot.get(attrKey) != null) {
    // Attribute is dirty
    return this._super(snapshot, json, key, attributes);
  } else {
    // Attribute is not dirty, not stored in inFlightAttributes
    // Ignore this attribute
    return;
  }
}