On: Learn from Haskell - Functional, Reusable JavaScri...

[jfager]

You don't need a map, just a reduce (foldl, really). Using underscore, no double calculation:

    _.reduce(arr, function(p1, p2) {
        var len = p2.firstName.length + p2.lastName.length;
        return (len > p1[1]) ? [p2, len] : p1;  
    }, 
    [null, -1]);

[wooby → jfager]

Also using underscore, with sortBy:

    _.chain(people)
    .sortBy(function(person) { 
      return person.firstName.length + person.lastName.length; })
    .last()
    .value()

[mhansen → wooby]

FYI, this isn't as general, but I think it shows off underscore quite nicely:

  _(people).max(function(person) {
    return person.firstName.length + person.lastName.length;
  });