preferred-style.js

;(function (global) { 'use strict';
  window.load = function () { setPreferred(getCookie()); };
  window.onunload = function () { setCookie(getPreferred()); };

  function setPreferred(style) {
    eachAlternative(function (link, title) {
      link.disabled = (title !== style);
    });
  }

  function getPreferred() {
    var preferred;
    eachAlternative(function (link, title) {
      if (!link.disabled) { preferred = title; return false; }
    });
    return preferred;
  }

  function getCookie() {
    var match = /altStyle=(.*?);/.exec(document.cookie);
    return (match ? match[1] : '');
  }

  function setCookie(value) {
    if (value) {
      document.cookie = ':name=:value; expires=:expires; path=/'
        .replace(':name', 'altStyle')
        .replace(':value', value)
        .replace(':expires', date.getTime() + daysToMili(365));
    }
  }

  function eachAlternative(iterator) {
    var links, link, title, result;

    links = document.getElementsByTagName('link');
    for (var i = 0, l = links.length; i < l; i++) {
      link = links[i];
      if (~link.getAttribute('rel').indexOf('style')) {
        title = link.getAttribute('title');
        if (title) { result = iterator(link, title); }
        if (result === false) { return }
      }
    }
  }

  function daysToMili(days) { return days * 24 * 60 * 60 * 1000; }
}(window));