angular2中可变长度数字的验证器或掩码

import { AbstractControl, ValidatorFn } from '@angular/forms';

export function variableLengthNumberValidator(length: number): ValidatorFn {
  return (control: AbstractControl): { [key: string]: any } | null => {
    const value = control.value;
    const isValid = /^\d+$/.test(value) && value.length === length;

    return isValid ? null : { variableLengthNumber: { value: control.value } };
  };
}

import { Component } from '@angular/core';
import { FormControl, FormGroup, Validators } from '@angular/forms';
import { variableLengthNumberValidator } from './variable-length-number.validator';

@Component({
  selector: 'app-my-form',
  template: `
    <form [formGroup]="myForm">
      <input type="text" formControlName="myNumber">
      <div *ngIf="myForm.get('myNumber').errors?.variableLengthNumber">
        Invalid variable length number!
      </div>
    </form>
  `,
})
export class MyFormComponent {
  myForm: FormGroup;

  constructor() {
    this.myForm = new FormGroup({
      myNumber: new FormControl('', [
        Validators.required,
        variableLengthNumberValidator(5),
      ]),
    });
  }
}