How do I pass JavaScript variables to PHP?

You cannot pass variable values from the current page JavaScript code to the current page PHP code… PHP code runs at the server side, and it doesn’t know anything about what is going on on the client side.
You need to pass variables to PHP code from the HTML form using another mechanism, such as submitting the form using the GET or POST methods.

‘ …; // and others
echo ‘

‘;
}
?>

Just save it in a cookie:
$(document).ready(function () {
createCookie(“height”, $(window).height(), “10”);
});

function createCookie(name, value, days) {
var expires;
if (days) {
var date = new Date();
date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
expires = “; expires=” + date.toGMTString();
}
else {
expires = “”;
}
document.cookie = escape(name) + “=” + escape(value) + expires + “; path=/”;
}

And then read it with PHP:

It’s not a pretty solution, but it works.