How To Read Cookie Set With PHP

I'm trying to read a cookie that I've set with php with javascript. The cookie is for storing the username when logging in to a site. If the cookie has been set I want the focus in the inline popup to target the password field so that the user doesn't have to tab down from the username field of the login form.

The php script stores the cookie perfectly:
if (isset($_POST['remember'])){
$expire = time()+60*60*24*30;
setcookie("login_username", $username, $expire);
echo $_COOKIE['login_username'];
} else {
if (isset($_COOKIE['login_username']) || isset($_COOKIE['password'])){
$expire = time()-3600;
setcookie("login_username", "", $expire);
}}

The javascript:
if (targetfocus == 'login_username'){
alert(readCookie('login_username'));
if (readCookie('login_username') == 'username'){
targetfocus = 'password';
}}
$("#"+targetfocus).focus();
...
function readCookie(name) {
var cookieName = name + "=";
var cookieArray = document.cookie.split(';');
for (var i = 0; i < cookieArray.length; i++){
var cookie = cookieArray[i];
while (cookie.charAt(0)==' '){
cookie = cookie.substring(1,cookie.length);
}if (cookie.indexOf(cookieName) == 0){
return cookie.substring(cookieName.length,cookie.length);
}return null;
}}

But when trying to read the cookie in the javascript code I receive null when I put an alert to the code. Why won't the javascript find the cookie? Is it because I'm running the site localhost on my laptop? Does that have an effect on cookies?