Sunday, August 22nd, 2010
One of the less known uses of external JavaScript is the ability to reference a PHP file instead of a .js file. This does seem to breach scripting etiquette, as we all "know" that server side and client side scripts are prohibited from interacting. Well, it turns out superficial exchange is allowed. Using external JavaScript, you’ll see how PHP and JavaScript can work together in a way you may not have thought possible, and to the great benefit of JavaScript.
The syntax to referencing a PHP file using external JavaScript is consistent enough with what we already know:
<script type="text/javascript" src="myscript.php"></script>
where myscript.php is either an absolute or relative path to a PHP script instead of the usual .js file. You can even pass parameters to the PHP script through the URL string:
<script type="text/javascript" src="myscript.php?param1=bob¶m2=thomas"></script>
Your PHP script can then get to these parameters using the global variable $HTTP_GET_VARS[]. So you’re probably wondering at this point: "So what’s the catch?" Well, there is no catch really, just a few limitations. Since we are invoking the PHP script indirectly and via JavaScript, the final output of the PHP script needs to be valid JavaScript. Think of it as a dynamic .js file, bounded by the same limitations as a regular .js file. A normal PHP script called inside a PHP page can output raw HTML and modify the source code of the page. The JavaScript invoked version obviously cannot, but don’t worry, there’s plenty of what it can do.
Here’s a basic example of a PHP script- ip.php – being called by external JavaScript to do something that JavaScript alone cannot:
<?
//"ip.php" example- display user IP address on any page
Header("content-type: application/x-javascript");
$serverIP=$_SERVER['REMOTE_ADDR'];
echo "document.write(\"Your IP address is: " . $serverIP . "\")";
?>
And once called by external JavaScript:
<script type="text/javascript" src="ip.php"></script>
Output: Your IP address is: 192.168.18.1
In the above, we have a normal PHP script that writes out the IP address of the visitor when referenced using external JavaScript, with two important details:
- A JavaScript header is sent at the very beginning to inform the page that our PHP script is outputting a JavaScript file.
- Since the final output of our PHP script needs to be a valid .js file, whatever the PHP outputs must conform to valid JavaScript syntax. So to display the IP address from the perspective of JavaScript, the echo function above includes
document.write() as part the content to send back to the page.
Notice how I didn’t output the JavaScript script tag itself <script></script>), as just like inside a regular .js file, this isn’t required nor valid.
The ability to reference a PHP script inside your external JavaScript can be very useful! It means your JavaScript now has access to once exclusive information on the server side, whether it’s the server time, the visitor’s IP address, a list of all the files within a certain directory, or mySQL database information. Now even regular HTML pages can utilize this dynamic information, as all they need is a JavaScript on the pages that in turn references the desired PHP script on your server or elsewhere.
Enjoy 😉
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