Extracting data for a tag cloud using Lazy.js

I've just started using Lazy.js, which is my first exposure to a "functional style" javascript library. I'm still utterly lost as to which of the hundred different functional javascript libraries to use, but so far I like Lazy.js, so I've used it to write a tag harvesting module for a blog engine project I'm working on. For anyone unfamiliar with Lazy.js (even moreso than I am) I'm under the impression its syntax is very similar to Underscore and Lodash.

getTagsWithCount: function(articles) {

  var tags = Lazy(articles).compact().pluck("attributes").pluck("tags").flatten().compact().sort().countBy()
  return tags // returns a Lazy.js Sequence
},

// Formats a Sequence of tag objects into the specific kind of JSON array for spoonfeeding to fussy baby tag-cloud.js
formatForTagCloud: function(tags) {
  var keysToJSON = tags.keys().map(function(x){return {"tagName": x, "count": tags.get(x)};}).toArray();
  var json = JSON.stringify(keysToJSON);
  return json;
}

Specific things I'm interested in/suspect I've done wrong:

• Is there a better way to dodge potential nulls in both the article array and in the tags of each articles than the double compact()? What's the performance impact of compact()? If it's light, should I make a habit of using it everywhere as a general way of avoiding null/undefined values in arrays?
• Is there a better way to do what I'm trying to do in formatForTagCloud? This function was purely to force my data into a format needed by a module I've actually ended up abandoning, but I'm presenting it here because writing it was a bit of a headache. Is there a different/better way of accessing both the key and the value of an ObjectLikeSequence? More to the point, I thought this would be a case where I could use either merge() or zip(), but neither of those worked, leaving me with this approach which I'm concerned would be considered a bit crude.
• I'm in the habit of creating variables then returning them, but I've seen other people write it the function so that the value is just returned without a variable being created first. Which is better? Are there performance benefits to be gained by doing the latter?
• Should I be putting newlines after some/all of my chained methods? Again, it's something I see, but I also sometimes find it a tiny bit confusing – but that's probably because I'm fairly new to the pattern.