问无法将数据从indexedDB传递给角度主题，以便在可观察的使用ngx db中使用。

EN

public userInfo = new Subject<any>();

 getData(){ 
    var db = new NgxIndexedDB('jwt', 1);    
    db.openDatabase(1).then(function() {
      db.getByKey('token', 1).then(
        (res) => {
            // Do something after the value was added
            console.log(res); //data populates in the console
            this.userInfo.next(res) // this step I receive undefined error
        },
        error => {
            console.log(error);
        }
    );
  }

watchUser(): Observable<any> {
  return this.userInfo.asObservable();        
};

getUserInfo(){
  this.watchUser().subscribe(res => console.log(res))
}