async-polyfill.js

function async(makeGenerator) {
  return (...args) => {
    var generator = makeGenerator.apply(this, args);

    function next(result) {
      // result => { done: [Boolean], value: [Object] }
      if (result.done) return Promise.resolve(result.value);

      return Promise.resolve(result.value).then((res) => {
        return next(generator.next(res.value));
      }).catch((err) => {
        return generator.throw(err);
      });
    }

    try {
      return next(generator.next());
    } catch (ex) {
      return Promise.reject(ex);
    }
  }
}