JavaScript is mainly used as a client side scripting language, while PHP is a server side technology. Unlike Java or ASP.Net, PHP doesn't have tools to make it work client side. That is why you need to combine JavaScript and PHP scripts to develop powerful web-applications.

One of the frequent problems is defining visitor’s screen resolution using JavaScript tools and passing this data to PHP-script. The following script provides solution for this problem:

<script type="text/javascript"> width = screen.width; height = screen.height; if (width > 0 && height >0) {     window.location.href = "http://localhost/main.php?width=" + width + "&height=" + height; } else      exit(); </script>

Copy and paste this code snippet in the text editor, save it as index.htm and run it in your browser. After this code has been executed, a user is automatically redirected to the main.php page where screen resolution is displayed in the browser window.

The main.php looks as follows:

<?php echo "<h1>Screen Resolution:</h1>"; echo "Width  : ".$_GET['width']."<br>"; echo "Height : ".$_GET['height']."<br>"; ?>

As you can see, passing JavaScript variables in PHP is similar to sending data using GET method.