I often use the [`promisify` method](https://nodejs.org/dist/latest-v8.x/docs/api/util.html#util_util_promisify_original), which converts a method with a callback signature (e.g. `fucntion fn(cb) { ... }`) to a method which returns a `Promise`. It can make the source code a lot cleaner and more compact. So far so good.

Slightly different, are methods which have a callback method, but the callback is called multiple times. In that case a `Promise` cannot do the trick, because a promise can only be executed once.

In theory, those methods could return a [`Subject`](https://rxjs-dev.firebaseapp.com/guide/subject). (e.g. a `BehaviorSubject`) which would then be fired multiple times.

This made me wondering:
**Is there a `subjectify` method somewhere, which can do this for me ?**

*For example: it could be useful when there is a method which parses a big document. To report on its progress, it could use a callback method. But wrapping it in a `Subject` could be more convenient.*