gistfile1.js

var pasv, pasvReqs;

pasvReqs = function(next, stop) {
    pasv = next;
};

pasvReqs(self.processPasv, function(err) { console.log(err) });

var processPasv = function(pasvData) {
        console.log("PASVDATA", pasvData);
    };

// -----

var enqueue = function(m, c) {
    pasv({
        mode: m,
        callback: c
    });
}

// Simplified version of https://github.com/Gozala/streamer/blob/queue/queue.js
function queue() {
  var next, buffer = Array.prototype.slice.call(arguments)

  function enqueue() {
    buffer.push.apply(buffer, arguments)
    if (next && buffer.length) {
      if (false !== next(buffer.shift())) enqueue()
    }
  }

  function stream($, stop) {
     next = $
     enqueue()
  }

  stream.enqueue = enqueue
  return stream
}

var pasvReqs = queue(....)

!function recur() {
    // Take first element from `pasvReqs` and process it via `processElement` black box that will call
   // `recur` once it's done to process next element from the `pasvReqs` queue.
    head(pasvReqs)(function(element) {
       processElement(element, recur)
    })
}()