handle.ts

/*
  Typescript erroring:
  ---
  Type 'Promise<(T | undefined)[] | [any, undefined]>' is not assignable to type 'Promise<[void | Error, void | T]>'.
  Type '(T | undefined)[] | [any, undefined]' is not assignable to type '[void | Error, void | T]'.
    Type '(T | undefined)[]' is not assignable to type '[void | Error, void | T]'.
      Target requires 2 element(s) but source may have fewer.ts(2322)
*/

export default function <T> (promise: Promise<T>): Promise<[Error | void, T | void]> {
  return promise
    .then((data) => ([undefined, data]))
    .catch((error) => ([error, undefined]))
}

/*
  Usage:
  const [err, res] = await handle(Axios.get('/api/foo'))
*/

Fixed! Thanks, @dlo! (https://twitter.com/dwlz/status/1340082549369036800)

export default function <T> (promise: Promise<T>): Promise<[Error | void, T | void]> {
  return promise
    .then((data: T) => [undefined, data] as [Error | void, T | void])
    .catch((error: Error) => [error, undefined]);
}