洋葱模型

class TaskPro {
  #tasks = [];
  #isRun = false;
  #currIndex = 0;
  /**
   * 添加任务
   * @param {Function} task
   */
  addTask(task) {
    this.#tasks.push(task);
  }
  //执行任务
  async run() {
    //不允许连续调用,需要等待上一次实例调用结束
    if (this.#isRun) return;
    this.#isRun = true;
    await this.#runTask();
  }
  //取出一个任务执行
  async #runTask() {
    //边界处理
    if (this.#runTaskBoundary()) return;
    const task = this.#tasks[this.#currIndex];
    //记录当前下标用于判定是否调用next
    const i = this.#currIndex;
    // 注入next
    await task(this.next.bind(this));
    const j = this.#currIndex;
    //如果没调next 则需要手动调用
    if (i === j) {
      await this.next();
    }
  }
  //执行任务时边界处理
  #runTaskBoundary() {
    if (this.#currIndex >= this.#tasks.length) {
      this.#isRun = false;
      this.#currIndex = 0;
      this.#tasks = [];
      return true;
    }
    return false;
  }
  async next() {
    this.#currIndex++;
    await this.#runTask();
  }
}

const t = new TaskPro();

t.addTask(async (next) => {
  console.log("task1 start");
  await next();
  console.log("task1 end");
});

t.addTask(() => {
  console.log("task2");
});
t.addTask(() => {
  console.log("task3");
});

t.run(); //输出 task1 start    task2   task3    task1 end