Delay Print Stylesheets Plugin

A few weeks ago I wrote a post in which I adapted an idea from a zOompf article to delay the loading of print stylesheets until after a web page has fully rendered. I finished that post with the following point/question:

Another question to ask is whether all this is actually worth the effort – even when reduced through automation. On Big Red Tin, the print.css is 595 bytes, the delay in rendering is negligible.

Chris and Jeff at Digging into WordPress picked up the article and posted it on their site. In turn it was picked up elsewhere and became the surprise hit of the summer at Big Red Tin. Not bad when one is shivering through a bitter Melbourne winter.

As a result of the interest, I decided to convert the code from the original post into a plugin and add it to the WordPress plugin directory.

Further Testing

As I warned in the original article, I’d tested the code in very limited circumstances and found it had worked. Fine for a code sample but not enough for a sub version-1.0-release plugin. Additional testing showed:

  1. Stylesheets intended for IE, through conditional comments, were loading in all browsers
  2. When loading multiple stylesheets, the correct order was not maintained in all browsers

If jQuery was available I wanted to use it for JavaScript event management otherwise I’d use purpose-written JavaScript. There’s no point, after all, of worrying about the rendering delay caused by 600-1000 bytes only to load a 71KB (or 24KB gzipped) file in its place.

Other things I wanted to do included:

  1. Put the PHP in a class to reduce the risk of clashing function/class names
  2. Put the JavaScript in its own namespace
  3. Keep the output code as small as possible

To support conditional comments for IE required adding each stylesheet within a separate <script> tag, using this method the output HTML takes the following form:

<script>
  // add global print.css
</script>
<!--[if IE 6]>
  <script type='text/javascript'>
    // add ie6 specific print.css
  </script>
<![endif]-->

This violates my aim to keep output as small as possible but footprint has to take second place to bug-free. I could have translated the code to use JavaScript conditional comments by translating the IE version to the JavaScript engine it uses but this could lead to future-proofing problems.

To maintain the order of stylesheets, I added each event to an array of functions and then used a single event to loop through the array of functions. If jQuery is used, I add multiple events because jQuery runs events on a first in first out basis.

Putting the PHP in a class and the JavaScript in its own namespace is fairly self-explanatory. Google is your friend if you wish to read up further on this.

Minimising the footprint was also a simple step. I wrote the JavaScript out in full with friendly variable names. Once I was happy with the code, I ran the code through the YUI JavaScript compressor, commented out the original JavaScript in the plugin file and output the compressed version in its place.

The JavaScript is output inline (within the HTML) to avoid additional HTTP requests. I was in two minds about this because browser caching is lost in the process. So it may change in a later version.

I’ve worked out another way to keep the footprint small. Rather than creating a function to pass the stylesheet’s URL and ID to brt_print.add(url, id), I wrote out the full function for each style sheet. I’ll fix that in the next release.

You can download the Delay Print CSS Plugin from the WordPress plugin repository.

Published by Peter Wilson

Peter Wilson is a Senior WordPress Engineer at Human Made and contributor to WordPress core. Peter has worked on the web for twenty years on everything from table based layouts in the 90s to enterprise grade CMS development. Peter’s a big fan of musical theater and often encourages his WordPress community colleagues to join him for a show or two in New York or in the West End.