RainerAtSpirit

(function () {
  var makeCallback = function(eventType, observer) {
    if (eventType === 'value') {
      return function(snap) {
        observer.onNext(snap);
      };
    } else {
      return function(snap, prevName) {
        // Wrap into an object, since we can only pass one argument through.
        observer.onNext({snapshot: snap, prevName: prevName});