Convert Scala async code to HighlandJS? Best practices?

I have a complex workflow I'm trying to get working in highlandjs. What makes it complex is (1) you need to transform a list-of-futures to future-of-list and (2) it's a sequence of async calls where the 3rd call depends on both the output of the 1st and 2nd.

It's working in Scala. Checkout this gist: https://gist.github.com/frankandrobot/ad857698f680aceb44e8

Unfortunately, I haven't been able to convert #preprocess1 into the highland equivalent.

• The highland version doesn't return anything (when calling #apply).
• A debug "hi from console" doesn't get fired either, so it's not getting called completely.
• The 3 async calls have been tested and are working.

UPDATE: yea, I'm in highlandjs nested hell. So pointers on how to get out of there would help.

UPDATE: It turns I wasn't passing "targets" to preprocess(). Doh. It's working as expected.
The question is now how can I clean this up? Best practices? Something about it doesn't seem right.

This is the JS code:

//this spits out a list of tags

this._fetchAllTags = _.wrapCallback(db.fetchAllTags);


//this also spits out a list of tags

this._fetchCombinedNearestNeighbors = function(targets, alltags) {

  var run_algorithm = _.wrapCallback(function(target, callback) {

           db.findKNearestNeighbors(target, alltags, callback)
        });

  return _(targets)
    .map(run_algorithm)
    .parallel(4)
    .sequence()
    .collect()
    .map(uniq); //get unique
};


//as you can see this depends on output of previous two async calls

this._fetchSSA = _.wrapCallback(function(allnearestneighbors, alltags, callback) {

  db.fetchSSA(allnearestneighbors, alltags, callback)
});


//can we clean this up?

this.preprocess = function() {

  return that._fetchAllTags()
    .flatMap(function(alltags) {

      return that._fetchCombinedNearestNeighbors(targets, alltags)
         .flatMap(function (allneighbors) {

         console.log('hi') 
         return that._fetchSSA(allneighbors, alltags);
      });
     });
};