TypeScript实现@End装饰器 强制链式调用末尾必须执行run方法

TypeScript 本身的装饰器仅负责运行时逻辑，没有原生支持类似 Java @End 注解的静态校验能力，但可以通过拆分类型完全实现漏写 run() 就触发编译报错的效果：

// 仅包含链式调用方法的类型，不暴露run方法
interface UserActionChain {
  attemptsTo(tasks: (() => Promise<void>)[]): UserActionChain
  expects(expectations: (() => Promise<void>)[]): UserActionChain
}

// 可执行的子类型，新增run方法
interface RunnableUser extends UserActionChain {
  run(): Promise<void>
}

class User implements RunnableUser {
  public name: string;
  public works: (() => Promise<void>)[];

  constructor(name: string) {
    this.name = name;
    this.works = [];
  }

  public attemptsTo(tasks: (() => Promise<void>)[]): UserActionChain {
    this.works.push(...tasks);
    return this;
  }

  public expects(expectations: (() => Promise<void>)[]): UserActionChain {
    this.works.push(...expectations);
    return this;
  }

  async run(): Promise<void> {
    for (const work of this.works) {
      await work();
    }
  }
}

// 工厂函数返回链式类型，屏蔽初始实例的run方法
function createUser(name: string): UserActionChain {
  return new User(name);
}

使用效果：

• 漏写run()直接编译报错：await createUser("Admin").attemptsTo([...]) 会提示类型不存在then方法，无法直接await
• 只有末尾添加run()才会通过类型校验：await createUser("Admin").attemptsTo([...]).run() 正常执行

如果不想额外写run()，可以让类实现PromiseLike接口，await实例时自动触发所有任务执行：

class User implements PromiseLike<void> {
  public name: string;
  public works: (() => Promise<void>)[];

  constructor(name: string) {
    this.name = name;
    this.works = [];
  }

  public attemptsTo(tasks: (() => Promise<void>)[]): this {
    this.works.push(...tasks);
    return this;
  }

  public expects(expectations: (() => Promise<void>)[]): this {
    this.works.push(...expectations);
    return this;
  }

  // 实现PromiseLike标准接口，await时自动执行
  then<TResult1 = void, TResult2 = never>(
    onfulfilled?: ((value: void) => TResult1 | PromiseLike<TResult1>) | null | undefined,
    onrejected?: ((reason: any) => TResult2 | PromiseLike<TResult2>) | null | undefined
  ): PromiseLike<TResult1 | TResult2> {
    const runAllTasks = async () => {
      for (const work of this.works) {
        await work();
      }
    };
    return runAllTasks().then(onfulfilled, onrejected);
  }
}

使用方式：

const admin = new User("Admin");
await admin
  .attemptsTo([EnterCredentials, Login])
  .expects([LoginSuccessfully])
  .attemptsTo([NavigateToUsersPage])
  .expects([SeeUsersList, AddNewUser]);
// 无需调用.run()，await时自动执行所有任务

内容的提问来源于stack exchange，提问作者HesamSe