Return typings for dynamic functions

Question

I have a function whose only logic is to execute a function that is passed in.

const funcRunner = async (func: Function) => {
   return await func()
}

I know that whatever the response of the function that is passed in will be the response of this same function.

However, this function return signature is inferred as Promise<any>. Is there any way to keep the response type of the original function?

const bool = async isExample(): Promise<boolean> => true;

// result should be boolean, not any
const result = await funcRunner(isExample);

Answer 1

You can define a generic type to run function:

type Runnable<T> = () => Promise<T>;

And then apply it for your funcRunner

async function funcRunner<T>(runnable: Runnable<T>): Promise<T> {
  return await runnable();
}

Optionally you can use inline typing:

async function funcRunner<T>(runnable: () => Promise<T>): Promise<T> {
  return await runnable();
}

Example usage:

async function example1(): Promise<number> {
  return 1;
}


funcRunner(example1)
    .then((result: number) => console.log(result))