Turns any function that returns a promise into a function that returns the promise with the value and error without throwing.

goify-promise-examples.ts

function add(a: number, b: number): Promise<number> {
  return Promise.resolve(a + b);
}

{
  const safeAdd = goify(add);

  const [val /* 7 */, err /* null */] = await safeAdd(2, 5);
}

function sub(a: number, b: number): Promise<number> {
  throw Error("Ha ha!");
  return Promise.resolve(a - b);
}

{
  const safeSub = goify(sub);

  const [val /* null */, err /* instanceof Error */] = await safeSub(6, 3); // DOES NOT THROW!

  if (err !== null) {
    console.log("Houston, we have a problem."); // this will log
  }
}

goify-promise.ts

/** @license Unlicense (Scroll to bottom for full license) */

// Included in license - by me
/** Unwraps a given `Promise` type into the value within it. */
type UnwrapPromise<T extends Promise<unknown>> = Parameters<
  Exclude<Parameters<T["then"]>[0], null | undefined>
>[0];

/**
 * Turns a function that returns a `Promise` into a safe, non-throwing function
 * that returns a tuple that contains the value and a possible error without
 * losing any typings via generics.
 */
export function goify<T extends (...args: any[]) => Promise<any>>(
  func: T
): (
  ...args: Parameters<T>
) => Promise<[UnwrapPromise<ReturnType<T>>, null | Error]> {
  return (...args: Parameters<T>) =>
    new Promise((resolve, _) => {
      try {
        func(...args).then((val) => {
          resolve([val, null]);
        });
      } catch (err: any) {
        resolve([null, err]);
      }
    });
}

/**
 * @license Unlicense
 *
 * This is free and unencumbered software released into the public domain.
 *
 * Anyone is free to copy, modify, publish, use, compile, sell, or
 * distribute this software, either in source code form or as a compiled
 * binary, for any purpose, commercial or non-commercial, and by any
 * means.
 *
 * In jurisdictions that recognize copyright laws, the author or authors
 * of this software dedicate any and all copyright interest in the
 * software to the public domain. We make this dedication for the benefit
 * of the public at large and to the detriment of our heirs and
 * successors. We intend this dedication to be an overt act of
 * relinquishment in perpetuity of all present and future rights to this
 * software under copyright law.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * For more information, please refer to <http://unlicense.org/>
 *
 */