gen-async.js

async function* createAsyncIterator() {
  const promise = [];
  const values = [];

  const subscription = this.materialize().subscribe(value => {
    values.push(value);
    promise.splice(0).forEach(r => r());
  });

  try {
    while (true) {
      while (values.length > 0) {
        const v = values.shift();
        if (v.kind == 'N') yield v.value;
        else if (v.kind == 'C') return;
        else if (v.kind == 'E') throw v.error;
      }
      await new Promise(r => promise.push(r));
    }
  } finally {
    subscription.unsubscribe();
  }
}