Why can you not return an object to Javascript's Array.map() and it map it properly?

I have two functions below (they are taken out of a larger script so assume everything is defined etc. self.sentenceObjs works great. It returns an object exactly like it's supposed to do. self.parseBodySections for some reason sets bodyJSON to an array of undefined even though self.sentenceObjs is returning perfect objects given the dom array of objects I want mapped. For some reason when I run dom.map(self.sentenceObjs) it returns undefined for each object. Any idea why this would be? Is there something with Array.map() that I missing?

  self.parseBodySections = function(dom, cb) {
    var bodyJSON = dom.map(self.sentenceObjs);
    console.log(bodyJSON); // prints: [ undefined, undefined, undefined, undefined, undefined ]

    return cb(null, bodyJSON);
  };

  self.sentenceObjs = function(section) {
    var paragraphToTextAndLinks = function(cb) {
      return self.paragraphToTextAndLinks(section.children, function(err, paragraphText, links) {
        if (err) {
          return cb(err);
        }

        return cb(null, paragraphText, links);
      });
    };

    return async.waterfall([
      paragraphToTextAndLinks,
      self.paragraphToSentences
    ],
    function(err, sentences, paragraphPlaintext) {
      var paragraph = {
        type: section.name,
        value: paragraphPlaintext,
        children: sentences
      };

      console.log(paragraph) // prints perfect object (too long to show here)

      return paragraph;
    });
  };