Can you use browser cookie? you can save score value in cookie and access it whenever you need? Read this on how to use cookies link https://developer.mozilla.org/en-US/docs/Web/API/document.cookie
To save to cookie like this:
document.cookie="score=54; expires=Thu, 18 Dec 2013 12:00:00 GMT";
In PHP you can read cookie
if(isset(($_COOKIE['score'])) {
$score = $_COOKIE['score'];
}
To Read cookie in JS:
var score = document.cookie;