问angularjs $watch watchExpression with promise将进入无限摘要循环

EN

$scope.$watch(function() {
var promise = MyService.getMethod();
promise.then(function(value){
  return value;
})
}, function(newValue, oldValue) {
console.log("new value:", newValue);
});

public getMethod(): angular.IPromise<any> {
  var deferred: angular.IDeferred<any>   = this.$q.defer();
  localforage.getItem(‘key’).then(function(value) {
    deferred.resolve(value);
  }).catch(function(err) {
    deferred.reject();
    console.log(err);
  });
  return deferred.promise;
}