expect.ts

type Expect<T> = {
    result: T;
    error: null;
} | {
    result: null;
    error: Error;
};

type Result<T> = Promise<T> | T;

const expect = async <T>(cb: Result<T>): Promise<Expect<T>> => {
    try {
        return { result: await cb, error: null };
    } catch (error) {

        if (error instanceof Error) {
            return { result: null, error: error };
        }

        return { result: null, error: new Error(`${error}`) };
    }
};

Usage example:

const result = await expect(fetch('google.com'));
if (result.error) {
  // handle error
}

const { result: response } = result;