code: function makeAccessedObserver() {
        return Observer(object, function(changes) {
          changes.forEach(({type, name}) => {
            var {names} = accessEntry;
            if (!names || type === 'update' && names.indexOf(name) !== -1)
              rerun();
          });
        });
      }
docs: Create an observer for changes in properties accessed during execution of this function.