Async/Await

async function asyncFn(filename) {
  const isError = false;

  const data = await externalServiceCall(filename + ".txt");

  if (isError) {
    return {
      error: Error("Error occured from fn2"),
      data: null,
    };
  } else {
    return {
      error: null,
      data,
    };
  }
}

Function calls :

const { error, data } = await asyncFn(FILE_NAME);
console.log(error, data);