Add a .execute as a .subscribe alternative

[Sawtaytoes]

I built an execute function to wrap RxJS observables for synchronous execution:

execute = () => {
  let outputValue

  const subscriber = (
    pipeline.subscribe(value => (
      outputValue = value
    ))
  )
  
  subscriber.unsubscribe()
  
  return outputValue
}

The .unsubscribe is only there in case someone puts a delay or something else async in the pipeline. You'd get undefined in that case which is expected.

It'd be nice if this were part of RxJS as an alternative to .subscribe, so I don't have to copy-paste it into every project that needs it.

While it seems useless, there are good reasons you might want to use RxJS for synchronous execution; although, I know it's not the standard use case since most people don't need it.

Since it's so simple to write one of these, I could keep copy-pasting it, but I think adding it natively in the library would be helpful to anyone that needs this functionality.

In the case of a BehaviorSubject, it already has a .value prop, but this is meant for synchronous execution where you don't have to worry about subscribing and unsubscribing.