function observable() {
    var _ref;

    var outerSubscribe = subscribe;
    return _ref = {
      /**
       * The minimal observable subscription method.
       * @param {Object} observer Any object that can be used as an observer.
       * The observer object should have a `next` method.
       * @returns {subscription} An object with an `unsubscribe` method that can
       * be used to unsubscribe the observable from the store, and prevent further
       * emission of values from the observable.
       */
      subscribe: function subscribe(observer) {
        if ((typeof observer === 'undefined' ? 'undefined' : _typeof(observer)) !== 'object' || observer === null) {
          throw new TypeError('Expected the observer to be an object.');
        }

        function observeState() {
          if (observer.next) {
            observer.next(getState());
          }
        }

        observeState();
        var unsubscribe = outerSubscribe(observeState);
        return { unsubscribe: unsubscribe };
      }
    }, _ref[result] = function () {
      return this;
    }, _ref;
  }
Interoperability point for observable/reactive libraries.
@returns {observable} A minimal observable of state changes.
For more information, see the observable proposal:
https://github.com/tc39/proposal-observable