存储PHP变量，以便稍后在同一脚本中的javascript中使用

我知道PHP发生在服务器端，一旦页面加载到浏览器中，就会执行javascript。我想知道如何在PHP中保存一个变量，以便以后在javascript函数中使用。

这一切都发生在同一个index.php脚本中：

    <? 
    // If session token exists, set javascript variable 
    if($_SESSION['token'] != null) 
    { 
        // Store session token as a variable 
        $sessionToken = $_SESSION['token']; 
    } 
    ?>
    <script>
      // Turn that PHP variable into a javascript variable
      var sessionToken = '<? echo $sessionToken; ?>';
    </script>
    <script>
      // This function works. It sends a string to the Unity web player
      // I'm trying to call it using a PHP variable as a parameter
      function SessionTokenToUnity($token) {
        // Send message to unity web player from browser
        u.getUnity().SendMessage("Settings", "MyFunction", $token);
      }
    </script>
    <script>
      // Call function with sessionToken which was set by PHP earlier as a parameter
      SessionTokenToUnity(sessionToken);
    </script>