generator2async.ts

const enum StepKey {
  next = 'next',
  throw = 'throw',
}

const generator2async = <
  P extends any[],
  T = unknown,
  TReturn = any,
  TNext = unknown,
>(
  generatorFunction: (...args: P) => Generator<T, TReturn, TNext>,
) => {
  return (...args: P) => {
    const generator = generatorFunction(...args);

    return new Promise<TReturn>((resolve, reject) => {
      (function step(key: StepKey, previousValue?: T) {
        let genResult: IteratorResult<T, TReturn>;

        try {
          genResult = generator[key](previousValue);
        } catch (err) {
          reject(err);
          return;
        }

        const { value, done } = genResult;

        if (done) {
          resolve(value);
          return;
        }

        Promise.resolve<T>(value).then(
          (e) => {
            step(StepKey.next, e);
          },
          (e) => {
            step(StepKey.throw, e);
          },
        );
      })(StepKey.next);
    });
  };
};