在angular 4中更改AsyncValidator的响应

import { AbstractControl, ValidationErrors } from '@angular/forms';
import { Observable } from 'rxjs';

export function customAsyncValidator(control: AbstractControl): Observable<ValidationErrors | null> {
  return new Observable(observer => {
    // 在这里进行异步验证逻辑
    // 如果验证通过，调用 observer.next(null)
    // 如果验证失败，调用 observer.next({ customError: true })
    // 最后调用 observer.complete() 结束验证

    // 示例：模拟异步验证
    setTimeout(() => {
      if (control.value === 'admin') {
        observer.next({ customError: true });
      } else {
        observer.next(null);
      }
      observer.complete();
    }, 2000);
  });
}

import { FormControl, FormGroup, Validators } from '@angular/forms';

const form = new FormGroup({
  username: new FormControl('', Validators.required, customAsyncValidator)
});