Get a PHP variable with javascript?

I have a javascript game running within a HTML5 canvas. Now I'd like to pass on a variable that is stored in an object in PHP to my program. What I'd like to have would be a function in my js like getVariable = function(){script that gets the variable from PHP and returns it as a string}

Any hints?

@Valentin - simply use javascript ajax call(Or jquery call if you like) to get the values from the php script. If your game has different values for different players you can start a session and persist the values across many calls to the script.For example -

Let say you want to get the health of the player from player.php which looks like 

 session_start();//start the session
 if(!isset($_SESSION['health']))
    $_SESSION['health'] = $var;//If there is no value for player health in the session
                               //initialize the default value
 switch($_GET['x']){
 case 'health' :
        echo $_SESSION['health'];
        break;
 default       :
        echo $var;
        break;
 }
?>

and the corresponding pure javascript would be - 

var health;
var xmlhttp;
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  } 
    xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    health=xmlhttp.responseText;
    }
  }
xmlhttp.open("GET","player.php?x=health",true);
xmlhttp.send();

You could do the same in a much simpler fashion using the awesome jQuery - 

var health;
var reqData=["x" : "health"];
var xhrObj = $.get("player.php",x)
    .done(function( response ) { 
      health=response;//The echo text from server
    })
    .fail(function() {
      alert('error'); 
    });

You can learn more about jquery and ajax here -->

jQuery API

www.w3schools.com/ajax/‎ for the ajax tutorial

Javascript and the browser don't care what language you're using on your server to generate the HTML/JS, all they care about is what is generated in the end.

To do what you're thinking, you'd have 2 ways to do it:

  1. Print the contents of the variable to the page when initially generating it.
  2. Use an AJAX call to a script on your server that echo's the value, then parse it in JavaScript. If you do this, though, you'd have to use the session or a database, or another means of keeping state between pages.