鸿蒙next 单例模式如何实现

class Util {
  // 私有构造
  private constructor() {
  }

  //私有静态属性
  private static instance?: Util = undefined

  //公共获取方法
  public static getInstance() {
    if (Util.instance == undefined) {
      Util.instance = new Util()
    }
    return Util.instance
  }
}

class Util {
  private static instance: Util = new Util()

  private constructor() {
  }

  public static getInstance(): Util {
    return Util.instance
  }
}