A quick and dirty jQuery implementation of Lenses. If you're into that sort of thing.

lens.js

(function ($) {
  $.lens = {};
  
  $.lens.of = function (get, set) {
    var lens = function (d) { return get(d); }
    lens.set = set;
    lens.modify = function (d, f) { return set(d, f(get(d))); }
    lens.compose = function (other_lens) {
      return $.lens.of(
        function (d) { return other_lens(get(d)); },
        function (d, v) { return set(d, other_lens.set(get(d), v)); }
      )
    }
    return lens;
  }

  $.lens.array = function (n) {
    return $.lens.of(
      function (a) { return a[n] },
      function (a, v) {
        var a = a.slice(0);
        a[n] = v;
        return a;
      }
    )
  }

  $.lens.obj = function (n) {
    return $.lens.of(
      function (o) { return o[n] },
      function (o, v) {
        var o = $.extend({}, o);
        o[n] = v;
        return o;
      }
    )
  }

  Array.lens = $.lens.array;
  Object.lens = $.lens.obj;
})(jQuery);

/*
var data = {
  'marvel' : ['hulk'],
  'dc' : ['super', 'man']
}

var lens = $.lens.obj('dc').compose($.lens.array(1))

var data2 = lens.set(data, "hero")
lens(data) // "man"
lens(data2) // "hero"

var data3 = lens.modify(data, function (s) { return s + "!!" })
$.lens.obj('dc')(data3) // ['super', 'man!!']
*/