Angular 异步 form 表单认证

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 asyncValidator(control: AbstractControl): {[key: string]: any} {
    return new Promise (resolve => {
      this.sharedService.checkUserName(control.value).subscribe((result:Result)=>
      {
        if(result.status)
        {
          resolve(null);
        }
        else{
          resolve({ validNumber: true });
        }
      },error=>
      {
        resolve({ validNumber: true });
      });
    });
  }

this.registerForm = formBuilder.group({
      userName:["",    
      Validators.required, 
      this.asyncValidator.bind(this)],