TypeScript type definition for function that wraps async function

Question

I have a function takes takes an arbitrary async function and returns the result of awaiting that async function, but wrapped in a try/catch which adds some additional logic. See ts playground.

const with401Redirection =
    <T extends (...args: any[]) => Promise<any>>(
        call: T
    ): ((...args: Parameters<T>) => ReturnType<T>) =>
    // @ts-expect-error
    async (...args: Parameters<T>): ReturnType<T> => {
        try {
            return await call(...args);
        } catch (error) {
            if ((error as any).httpStatus === 401) {
                // do some stuff here
            }

            throw error;
        }
    };

interface User {
    id: string;
    name: string;
}

interface ItemPayload {
    field1: string;
    field2: string;
}

interface ItemResponse {
    id: string;
    field1: string;
    field2: string;
}

const client = {
    get<ResponseType>(url: string): Promise<ResponseType> {
        // logic to hit server and return result here
        return '' as any;
    },
    post<ResponseType>(url: string, body: Record<string, any>): Promise<ResponseType> {
        // logic to hit server and return result here
        return '' as any;
    }
};

const getUser = with401Redirection(() =>
    client.get<User>('url_1')
);

const saveItem = with401Redirection((body: ItemPayload) =>
    client.post<ItemResponse>('url_2', body)
);

I feel like the // @ts-expect-error in with401Redirection shouldn't be necessary -- how can I remove it or generally clean up the typing of the with401Redirection function? Keep in mind I want to maintain the fact that the getUser and saveItem functions have their types automatically inferred for me.

jsejcksn · Accepted Answer · 2021-11-13 00:21:15Z

5

Try this:

TS Playground link

type Awaited<T> = T extends PromiseLike<infer U> ? Awaited<U> : T;
type AsyncFn = (...args: any[]) => Promise<any>;

function with401Redirection <T extends AsyncFn>(call: T): (...args: Parameters<T>) => Promise<Awaited<ReturnType<T>>> {
    return async (...args: Parameters<T>) => {
        try {
            return await call(...args);
        }
        catch (exception) {
            if (typeof exception === 'object' && (exception as any)?.httpStatus === 401) {
                // do some stuff here
            }
            throw exception;
        }
    };
}

Read about the actual, upcoming Awaited type in TS 4.5:

https://devblogs.microsoft.com/typescript/announcing-typescript-4-5-beta/#the-awaited-type-and-promise-improvements

answered Nov 13, 2021 at 0:21

jsejcksn

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2 Comments

David Over a year ago

How could I make this work if I want to chain nested async function wrappers?

jsejcksn Over a year ago

^ @David Please ask a new question.

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