AngularFire2 Child_added event return all data again

Is the child_added event in angularfire is different in child_added on firebase?

why angularfire return all list including value after child_added while in firebase it only return la

 this.userList = this.room.getAllUser();
    this.userList.snapshotChanges()
      .subscribe(actions => {
         console.log(actions);
        actions.forEach(action => {
          console.log(action.type);
          console.log(action.key);
          console.log(action.payload.val());
        })

Do I need to scan again the response and compare the key if in array ? before pushing it ?