When multiple property changes provoke a single change method, arguments to that method are incorrect

[sorvell]

Now that multiple property changes can provoke a single property change method call, the arguments to the property change method must include all the old and new values and probably also the names of the properties that have changed.

[sorvell]

For example:

observe: {
  foo: 'invalidate',
  bar: 'invadliate'
},
// oldValue will be one of foo or bar but we need to pass both and should probably pass oldValues, newValues, and property names
invalidate: function(oldValue) {
}

[sorvell]

@rafaelw We are currently using a single CompoundPathObserver (cpo) to watch properties. For the case shown above, it seems like we want a separate cpo to track this set of changes. Otherwise, the master cpo has to do significant work to pass along the right set of changes, work that cpo exists to do. wdyt?

@frankiefu was concerned that the cpo api (changeHandler(newValues, oldValues, changes, paths) ) is too cumbersome and that we want to sugar it somewhat. He wanted something like changeHandler(changes) where changes would be an object with changes[path].oldValue, changes[path].newValue, changes[path].changed.

[rafaelw]

I think the task here is to define what the callback API should do. I seriously doubt the solution requires more than one CompoundObserver

[tjsavage]

Closing this issue due to age and the release of version 1 of Polymer - please feel free to re-open if this is incorrect.