Accessibility - Web Standards: Mastering HTML5, CSS3, and XML - page 362

function getActiveTheme() {
var i, a;
for(i = 0; (a = document.getElementsByTagName("link")[i]); i++) {
if(a.getAttribute("rel").indexOf("style") != -1 && a.getAttribute("title") && 
!a.disabled) return a.getAttribute("title");
}
return null;
}
function getPreferredTheme() {
var i, a;
for (i = 0; (a = document.getElementsByTagName("link")[i]); i++) {
if (a.getAttribute("rel").indexOf("style") != -1
&& a.getAttribute("rel").indexOf("alt") == -1
&& a.getAttribute("title")
) return a.getAttribute("title");
}
return null;
}
function createCookie(name,value,days) {
if (days) {
var date = new Date();
date.setTime(date.getTime() + (days*24*60*60*1000));
var expires = "; expires=" + date.toGMTString();
}
else expires = "";
document.cookie = name + "=" + value + expires + "; path=/";
}
function readCookie(name) {
var nameEQ = name + "=";
var ca = document.cookie.split(';');
for (var i = 0; i < ca.length; i++) {
var c = ca[i];
while (c.charAt(0)==' ') c = c.substring(1, c.length);
if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length, c.length);
}
return null;
}
window.onload = function(e) {
var cookie = readCookie("style");
var title = cookie ? cookie : getPreferredTheme();
setActiveTheme(title);
}