Polyfill for `Promise.witResolvers()` in TypeScript

polyfill.ts

Promise.withResolvers ??= function <T>() {
  let resolve: PromiseWithResolvers<T>["resolve"];
  let reject: PromiseWithResolvers<T>["reject"];
  const promise = new Promise<T>((res, rej) => {
    resolve = res;
    reject = rej;
  });
  return { promise, resolve: resolve!, reject: reject! };
};