Here is an example of reducing sublists to their sums using functional JavaScript.

reduceSubLists.js

_.chain([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
  // Grab each sublist and...
  .map(function(sublist) {
    // Sum each of its elements up!
    return _.reduce(sublist, function(total, num) {
      return total += num;
    });
  }).value();