attempt.ts

attempt.ts

/** Make sure that an unknown object is an error. If it's not, wrap it in an
 * error with a useful inspection message */
export function ensureError(err: unknown): Error {
  if (err instanceof Error) {
    return err
  }

  let data: string

  try {
    data = JSON.stringify(err)

    if (data.length > 256) {
      data = data.slice(0, 255) + '…'
    }
  } catch (err) {
    data = `(failed to JSON.stringify: "${err}") `
  }

  return new Error(`Non-error object was thrown or rejected: ${data}`, {
    cause: err,
  })
}

/** Result discriminated union */
type Result<Ok, Err> = [Ok, null] | [null, Err]

/** Runs a sync/async function and wraps its result/error in a {@link Result}
 * discriminated union. To be removed when
 * https://github.com/arthurfiorette/proposal-try-operator is available */
export function attempt<Ok, Err extends Error = Error>(fn: () => Ok) {
  type AttemptReturnType<Ok, Err> = Ok extends Promise<infer ResolvedOk>
    ? Promise<Result<ResolvedOk, Err>>
    : Result<Ok, Err>

  try {
    const result = fn()

    if (result instanceof Promise) {
      return result
        .then((resolved) => [resolved, null])
        .catch((e) => {
          return [null, ensureError(e)]
        }) as AttemptReturnType<Ok, Err>
    } else {
      return [result, null] as AttemptReturnType<Ok, Err>
    }
  } catch (e) {
    return [null, ensureError(e)] as AttemptReturnType<Ok, Err>
  }
}