export interface ValidatorFn {
  (c: AbstractControl): ValidationErrors | null;
}

export declare type ValidationErrors = {
  [key: string]: any;
};

export declare class FormControl extends AbstractControl {
  constructor(formState?: any, validator?: ValidatorFn | ValidatorFn[] | null, asyncValidator?: AsyncValidatorFn | AsyncValidatorFn[] | null);

static EMAIL_REG = new RegExp('\\w[-\\w.+]*@([A-Za-z0-9][-A-Za-z0-9]+\.)+[A-Za-z]{2,14}');
static email(): ValidatorFn {
  return (control: AbstractControl): { [key: string]: any } => { ①
   if (!EMAIL_REG.test(control.value)) { ②
    return { ③
     errMsg: '请输入正确的邮箱地址'
    };
   }
   return {}; ④
  };
 }

<p *ngIf = "!email.valid && email.touched">{{email.errors.errMsg}}</p>

static EMAIL_REG = new RegExp('\\w[-\\w.+]*@([A-Za-z0-9][-A-Za-z0-9]+\.)+[A-Za-z]{2,14}');
static email(emailForm: FormControl): ValidatorFn { ①
  return (control: AbstractControl): { [key: string]: any } => { 
   if (emailForm.value !== control.value ) { 
    return { 
     errMsg: '请输入相同邮箱地址'
    };
   }
   return {}; 
  };
 }

email = new FormControl('', email())
email2 = new FormControl('', email(email))