Make your pages load faster by combining and compressing javascript and css files

from: http://rakaz.nl/item/make_your_pages_load_faster_by_combining_and_compressing_javascript_and_css_files

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About six months ago I noticed the pages generated by the content management system were in itself very clean and small, but that these pages still took a long time to load for new visitors. Even on a fast internet connection it took more than 8 seconds to load a basically empty page. The server generated the page in about 350ms, so that wasn't the problem. The problem turned out to be a combination of two things: each page used more than 12 different css files because each plugin supplied its own css definitions and because the use of the rather large prototype and scriptaculous javascript libraries which also consists of a couple of different files. Now that an article about the same problem featured on the Yahoo! User Interface blog, I decided to make my solution public, so others can benefit from it.

The solution turned out the be simple, combine all the different files into a single large file and compress that file using gzip. Unfortunately, if you do this manually you are going to run into maintenance problems. That single compressed file is no longer editable. So after editing one of the original source files you will have to recombine it with the other files and re-compress it.

Instead of going for the easy - but hard to maintain - solution I decided to automate the process and thanks to a small PHP script and some clever URL rewriting I now have an easy to maintain method to speed up the loading of pages that use many or large css and javascript files.

The idea is that you have one directory for css files and one directory for javascript files on your server. If you rewrite the URLs that point to these directories to a small script that intercepts the requests for those files. The script loads the file from disk and compresses it using gzip. It then sends that compressed file back to the browser. Given that javascript and css files compress really well this will greatly decrease the size of the data that is going to be transferred and thus decrease the time needed to download these files. Because this works completely transparently you do not need to change anything in your existing code.

But there is more. Compressing the files will decrease the size of the data that needs to be transferred, it does not solve the problem that the browser can only download a limited number of files at the same time. If you have many different files that need to be loaded the browser will not optimally use the bandwidth it has access to. It will request some files from the server and wait until those files are retrieved before the rest of the files are requested. The solution to this problem is to combine all those different files into one large file. And this is exactly what the script tries to do. You can concatenate different files by simply adding the names of the other files to the URL of the first file.

Take for example the following URLs:
http://www.creatype.nl/javascript/prototype.js
http://www.creatype.nl/javascript/builder.js
http://www.creatype.nl/javascript/effects.js
http://www.creatype.nl/javascript/dragdrop.js
http://www.creatype.nl/javascript/slider.js

You can combine all these files to a single file by simply changing the URL to:
http://www.creatype.nl/javascript/prototype.js,builder.js,effects.js,dragdrop.js,slider.js

The script will intercept the attempt to retrieve something from the javascript directory and will notice that you want to fetch multiple files at once. It will then concatenate the requested files, compress it and send it as one to the browser. Also notice that I include the files that come with scriptaculous manually and I do not use the scriptaculous.js file like you normally would. The reason for this is that scriptaculous.js loads each javascript file individually. If I use the scriptaculous.js file I will get the benefit of compression, but the different files won't be combined into a single file.

Unfortunately I noticed a nasty side effect of the combination of these two methods. If you combine many files the resulting files can be come quite large. Compressing those files takes some time and on a busy server that time will become large enough to negate a significant portion of the improvements you made earlier. But this problem can also be solved by simply adding a cache that stores an already combined and compressed version of the files. The cached version is automatically created the first time that particular combination of files is used and used every time - as long as the files are not changed. The result is that once the cache is created there is almost no overhead and the compressed file is delivered almost instantly.

I've done some informal testing on my own website and I did get some impressive results. Before this script was added to my website you needed to download 8 javascript files, in total 168 Kb - the prototype and scriptaculous libraries. On average this took about 1905 ms. After installing this script you now need to download only a single file of 37 Kb which only takes around 400 ms. Your results may vary of course, but given that it shaved 1.5 seconds of a total loading time of 3.5 seconds, this script almost cut the time needed to load a page on my weblog in two.

Configurating this script is easy. First you need to download and configure the combine.php script. By default this script look in the javascript and css directory in the root of your website, but if you are currently using different directories you can change these values at the top of the combine.php script. Upload the combine.php script to the root of your website. Secondly you need to create a cache directory that is writable by the web server. Again, by default this script will look for the cache directory in the root of the website, but you can change this in the combine.php script. Finally you need to create or modify your .htaccess file. If you do not have a .htaccess file you can create it in the root of your website and add the following lines. If you already have an preexisting .htaccess file you can simply add the following lines to the file:

RewriteEngine On
RewriteBase /
RewriteRule ^css/(.*/.css) /combine.php?type=css&files=$1
RewriteRule ^javascript/(.*/.js) /combine.php?type=javascript&files=$1

Note: if your preexisting .htaccess file already uses URL rewriting you do not need to add the first two lines. You can simply add the last two lines to the bottom of the .htaccess file.