You're not using indexOf
correctly.
function getCookie(cookieName) {
var name = cookieName + "=";
var ca = document.cookie.split(';');
for (var i = 0; i < ca.length; i++) {
var c = ca[i].trim();
if ((c.indexOf(name)) == 0) {
alert("found");
return c.substr(name.length);
}
}
alert("not found");
return null;
}