Typescript asynchronous decorators decorate synchronous methods #48022

GO-DIE · 2022-02-24T08:23:07Z

How to correctly identify synchronous methods that have been modified to be asynchronous when using asynchronous decorators to decorate synchronous methods.

💻 Code

function AsyncDecorator() {
  return (target: any, propertyKey: string, descriptor: PropertyDescriptor) => {
    const originalMethod = descriptor.value;
    descriptor.value = async function (...args: any[]) {
      await sleep(100);
      const result = await originalMethod.apply(this, args);
      return result;
    };
    return descriptor;
  };
}

async function sleep(ms: number) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

class Test {
  // This function appears to be a synchronous function, but has been changed to an asynchronous function by an asynchronous decorator, but I didn't know that
  @AsyncDecorator()
  fun(): string {
    return 'Hello World!';
  }
}

const result = new Test().fun();
console.log(result); // Expect results: Hello World!  Actual result: Promise {<pending>}

🙁 Actual behavior

Promise {<pending>}

🙂 Expected behavior

Hello World!

MartinJohns · 2022-02-24T08:36:04Z

You need #4881, which is not supported (and likely won't be for quite a while, at least until the decorator proposal is finally finished).

jcalz · 2022-02-24T16:21:49Z

Is this a bug report or a question? If it's a bug report you didn't fill out the full template; could you go back and do that?. If it's a question, then it doesn't belong here; maybe Stack Overflow is a better place, oh wait, you already opened a question there. 😃

In any case I'm not sure why your expected behavior is "Hello World!" given that you are logging a promise to the console, seemingly intentionally. I think your real expected behavior is that new Test().fun() should be seen as a Promise<string> instead of as a string and that the compiler should complain if you write, say, new Test().fun().toUppercase() instead of new Test().fun().then(x => x.toUpperCase()).

typescript-bot · 2022-02-27T18:00:05Z

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.

RyanCavanaugh added the Duplicate An existing issue was already created label Feb 24, 2022

typescript-bot closed this as completed Feb 27, 2022

Typescript asynchronous decorators decorate synchronous methods #48022

Typescript asynchronous decorators decorate synchronous methods #48022

GO-DIE commented Feb 24, 2022

MartinJohns commented Feb 24, 2022

jcalz commented Feb 24, 2022

typescript-bot commented Feb 27, 2022

Typescript asynchronous decorators decorate synchronous methods #48022

Typescript asynchronous decorators decorate synchronous methods #48022

Comments

GO-DIE commented Feb 24, 2022

💻 Code

🙁 Actual behavior

🙂 Expected behavior

MartinJohns commented Feb 24, 2022

jcalz commented Feb 24, 2022

typescript-bot commented Feb 27, 2022