async-gen.js

import { Observable } from "rxjs";

Observable.prototype[Symbol.asyncIterator] = createAsyncIterator;

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

  const values = [];
  let done = false;
  let error = null;

  const subscription = this.subscribe({
    next(value) {
      values.push(value);
      promise.splice(0).forEach(r => r());
    },
    error(err) {
      error = err;
      promise.splice(0).forEach(r => r());
    },
    complete() {
      done = true;
      promise.splice(0).forEach(r => r());
    },
  });

  try {
    while (true) {
      while (values.length > 0) yield values.shift();
      if (error) throw error;
      if (done) break;
      await new Promise(r => promise.push(r));
    }
  } finally {
    subscription.unsubscribe();
  }
}