obs-async-iterator.js

function createAsyncIterator() {
  const promises = [];
  const values = [];

  this.subscribe({
    next(value) {
      if (promises.length > 0) {
        promises.shift().resolve({ value, done: false });
      } else {
        values.push(value);
      }
    }
  });
  return {
    next() {
      if (values.length > 0) {
        return { value: values.shift(), done: false };
      }
      return new Promise((resolve, reject) => {
        promises.push({ resolve, reject });
      });
    }
  };
}