How can my TypeScript method be typed as string if it is async (and thus is forced to return a Promise)?

Question

I am writing some TypeScript classes that fetch resources by their reference - everyday things like if the resource is a file, the reference is the pathname; if the resource is a web service, the reference is the URL, etc.

In this world, references and resources are always strings.

So I have some code like this:

/**
 * Calls an HTTP endpoint
 */

export default class CallEndpoint {

    getResource(reference: string): string {
        return fetch(reference);
    }

}

I want to define getResource as string, but eagle-eyed readers know I can't: fetch() is async, so getResource can't be defined as returning a string.

I've tried to do some research on this question, and the answer is "properly work with asynchrony as shown in the duplicates linked", which I feel does not answer my question, and brings me to a dead end.

My editor is TypeScript-aware and shows there is an error with the above code. If I do this, it is happy:

export default class CallEndpoint {

    async getResource(reference: string) {
        return await fetch(reference);
    }

}

However, now I am not happy, since I want this to be explicitly marked as returning a string. Indeed, I have written a generic cache wrapper, which I make use of in a child class (CallEndpointCached) and my interface requires this method to return a string (because, well, a resource is always a string). Do I have to make do with this being essentially untyped?

In other words, is there a way I can block in this function, so that I can obtain a string result that respects the function return type I have chosen?

Update

I suppose the async/await is pointless here, but my editor says it still can't be typed. I think it should be:

export default class CallEndpoint {

    getResource(reference: string) {
        return fetch(reference);
    }

}

Something can await this downstream, I guess.

Footnote

(I've bumped into Promises and async several times, and unfortunately I struggle to fully understand them every time. While I am aware of the performance benefits of async, the stall on developer productivity strikes me as more than sapping those benefits, especially where the system is not in need of optimisation).

Answer 1

async methods always return promises. Any return value is wrapped in a Promise<T>. So if you have a method that returns a value of type string, then the return value of that method is Promise<string>.

especially where the system is not in need of optimisation

async does not mean "faster". It means "responsive". Asynchronous code is required on the UI side for the browser window to remain responsive (avoid the "frozen tab" dialog), and it's required on the Node.js side for the server to remain responsive (handle more than one request at a time).