tryit.ts

/**
 * This is really a _best guess_ promise checking. You
 * should probably use Promise.resolve(value) to be 100%
 * sure you're handling it correctly.
 */
export const isPromise = (value: any): value is Promise<any> => {
  if (!value) return false
  if (!value.then) return false
  if (!isFunction(value.then)) return false
  return true
}

/**
 * A helper to try an async function without forking
 * the control flow. Returns an error first callback _like_
 * array response as [Error, result]
 */
export const tryit = <Args extends any[], Return>(
  func: (...args: Args) => Return
) => {
  return (
    ...args: Args
  ): Return extends Promise<any>
    ? Promise<[Error, undefined] | [undefined, Awaited<Return>]>
    : [Error, undefined] | [undefined, Return] => {
    try {
      const result = func(...args)
      if (isPromise(result)) {
        return result
          .then(value => [undefined, value])
          .catch(err => [err, undefined]) as Return extends Promise<any>
          ? Promise<[Error, undefined] | [undefined, Awaited<Return>]>
          : [Error, undefined] | [undefined, Return]
      }
      return [undefined, result] as Return extends Promise<any>
        ? Promise<[Error, undefined] | [undefined, Awaited<Return>]>
        : [Error, undefined] | [undefined, Return]
    } catch (err) {
      return [err as any, undefined] as Return extends Promise<any>
        ? Promise<[Error, undefined] | [undefined, Awaited<Return>]>
        : [Error, undefined] | [undefined, Return]
    }
  }
}