aggregate multiple event emitter events + data onto a single event emitter that emits data events on change.
var es =ee1 =ee2 =esee1esee2esee1 // since "one" and "two" are undefined, it'll clear those states
listen to an
eventName. when that emitter emits that event name,
it will update the state object. the state object will then emit a
containing the current state.