Accessing source observable from outside Rx.Observable.prototype

Question

I am having trouble figuring out how to access the source observable, in this scheme (just trying to figure out how to this without modifying Rx.Observable.prototype):

      q.drain()
        .flatMap(function(val){
            return q.backpressure(val, function(cb){
                   setTimeout(cb,1000);
            });
        })

We call backpressure as a method on the Queue prototype:

Queue.prototype.backpressure = function(val, fn){

    const source = ? // I don't know how to access the source observable...

    return Rx.Observable.create(sub => {

        return source.subscribe(val => {

                fn.call(source, val, function(err, val){
                    if(err){
                        sub.error(err);
                    }
                    else{
                        sub.next(val);
                    }

                });
            },
            // be sure to handle errors and completions as appropriate and
            // send them along
            err => sub.error(err),
            () => sub.complete());

    });
};

but the problem is I don't know if I can access the source observable in this scheme - the correct value for source is certainly not the this value inside the prototype because that belongs to the queue instance. My only hope I think is somehow to pass the source observable directly into the backpressure method. Anyone know how I can this? I don't mind putting this function elsewhere, it doesn't have to be a method on queue, but I think the same problem will exist either way.

If it helps, the value for this inside the flatMap function (if you use a regular function instead of an arrow function) is a MergeMapSubcriber object, see:

However, after experimenting, I don't believe that the MergeMapSubcriber value is the one I want to use as my source; my source should be an Observable TMK, not a Subscriber.

Answer 1

Have you thought about putting it on Observable prototype?

Observable.prototype.backpressure = function(queue, fn){
  const source = this;

  return this.flatMap(function(val){
    return Rx.Observable.create(sub => {

      return source.subscribe...
    });
  })
};

Then for queue:

q.drain()
  .backpressure(q, function(cb) {
    setTimeout(cb,1000);
  });