In PHP.js, $_COOKIE is a function ;-)
function $_COOKIE(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 decodeURIComponent(c.substring(nameEQ.length,c.length).replace(/\+/g, '%20'));
}
return null;
}