PHP: How to add expire headers for external scripts

The problem with external scripts

When using an external service as such as Google Analytics, you are often required to include external JavaScript files into your own website.

While this isn’t a problem per se, you obviously don’t have as much control over those files than over files hosted on your own server. This is especially problematic since you should always set an expire header to static files in order to leverage browser caching and optimize your website speed.

Google PageSpeed Insight will recommend you to do so:

The solution: Adding expire headers to external scripts

So what we need to do is to import all the .js files dynamically into our website. To do so, we’ll use PHP and the file_get_contents() function.

The first thing to do is to locate the external script:

<script type="text/javascript" src="https://ssl.google-analytics.com/ga.js"></script>

The next step is to create a .php file. Let’s call it externaljs.php. Insert the following code in it:

<?php

$files = array(
	'ga.js' => 'https://ssl.google-analytics.com/ga.js',
	'bsa.js' => 'https://s3.buysellads.com/ac/bsa.js',
	'pro.js' => 'https://s3.buysellads.com/ac/pro.js'
);

if(isset($files[$_GET['file']])) {
	if ($files[$_GET['file']] == 'ga.js'){
		header('Expires: '.gmdate('D, d M Y H:i:s \G\M\T', time() + ((60 * 60) * 48))); // 2 days for GA
	} else {
		header('Expires: '.gmdate('D, d M Y H:i:s \G\M\T', time() + (60 * 60))); // Default set to 1 hour
	}

	echo file_get_contents($files[$_GET['file']]);
}

?>

Let’s have a look at the code:

• Lines 3 to 7: An array containing the accepted files is created. This is super important since otherwise any file could be embedded into your site, leading to potential security problems.
• Lines 9 to 14: Since we need to adjust the expiring time for every script, we need a conditional statement to do so.
• Line 16: If the script passed out as a GET parameter is found in our array, we can now safely display it.

You’ll need to adjust the code and enter the URLs of your external scripts. Once done, just upload it onto your server. If you’re using WordPress, it’s a good idea to put the file in your theme folder.

Then, simply replace the external .js call and replace it by a call to your externaljs.php file, as shown below:

<script type="text/javascript" src="externaljs.php?url=ga.js"></script>

And you’re done. You can now dynamically import external .js file on your server and therefore, set the right expire header for each script.