JavaScript Style Sheets

One of the privileges I have experienced in my professional life is having worked with Jeremy Keith of Clearleft. I learned a lot from the author and web developer from our interactions and by studying his code.

Jeremy is a fan of graceful degradation and ensures that a site will function just fine without JavaScript browser support. However, instead of mingling JS and non-JS styles together, he employs a particularly clever technique. He puts the standard styles in the standard CSS file. But just as his sites provide print and mobile stylesheets for printers and mobile devices, he also provides one for JS-enabled browsers. This has two nice side-effects: (1) better CSS organization and (2) CSS that is applied immediately, not after JS has had an effect on the DOM.

One example is a thumbnails carousel he designed. If the browser does not have JS support, the thumbnails are arranged in a grid. If the client does support JS, he wraps-up the thumbnails in a single row inside a horizontally-scrolling carousel, so they can be browsed left to right. The carousel presentation of the thumbnails requires a different set of CSS rules, which override the vanilla styles.

Here’s how he pulls off the wiring-up of a JavaScript CSS style sheet:

  <script type="text/javascript">document.write('<link rel="stylesheet" href="/stylesheets/javascript.css" media="screen,projection">');</script>

Any site I’m involved in will be following suit.

Thanks, Jeremy!

Specificity, Eames. Specificity?!

Way-back-when, I suggested that CSS authors use classes as much as possible. It was a foggy idea at the time, but, thankfully, someone important stumbled-upon the same concept, and codified it. Around the same time, it started to become popular for developers to consolidate CSS and JavaScript into two files for their sites. This technique saves HTTP requests, speeding-up users’ experiences of your site.

Now that I have had a few years to use these techniques, I’m happy to report they work beautifully; that is, until you have large CSS and JavaScript files that take a long time to download. Long downloads risk new visitors’ first impressions. You want it them to be wowed. A slow introduction doesn’t wow.

Large CSS and JavaScript files are often symptomatic of defining a heterogeneous set of styles or behaviors for very particular elements on very particular pages. In other words, styles and behaviors that aren’t re-used; ones that don’t scale. Here are some straightforward techniques to lighten those two global files:

Page-specific styles. I see CSS as a way to define general styles that affect large portions of a site (using classes). If you want to do something really, really special on a particular page, just put it inside the handful of elements that want to be different as inline styles. (ID selectors are a dying breed.) There’s no need to define rules in a global style sheet if they’re not really global. If the page has a lot of inline styles, and they are making the markup unmanageable, you can always extract the styles into a page-specific stylesheet. One extra HTTP request on one page (or a handful of pages) won’t kill you or your users.
Page-specific JavaScript. Users may never even get to some pages; why slow down their first request to your site to grab JavaScript for them? Don’t be ashamed to slap-in a JavaScript script block at the bottom of your page’s markup.

There is a continuum between two consolidated files for all your CSS and JavaScript and obtrusive CSS and JavaScript. As with many other things in life, you’ve gotta’ find the healthy balance.

Document Domain

Every few years I run into an issue with JavaScript-based rich text editors and spellcheckers when they spawn pop-ups. The pop-ups open but don’t function.

If I open my Firebug console in the pop-up, I see something like:

Permission denied for <http://assets2.mysitedomain.com> (document.domain has not been set) to get property Window.tinymce from <http://www.mysitedomain.com> (document.domain has not been set).

Chrome’s console, shows a similar error:

Unsafe JavaScript attempt to access frame with URL http://www.mysitedomain.com/mypage from frame with URL http://assets2.mysitedomain.com/javascripts/lib/tiny_mce/themes/advanced/source_editor.htm. Domains, protocols and ports must match.

In this case, TinyMCE‘s HTML plugin is running-up against JavaScript’s same origin policy because I’m serving assets (and therefore TinyMCE pop-ups) from a different fully-qualified domain name than the page TinyMCE is being embedded in. When not explicitly set, my site’s pages will default to something like www.mysitedomain.com and TinyMCE’s document domain will default to assets2.mysitedomain.com.

The simple fix is to bump up the document domain on my site’s pages to just mysitedomain.com. I do this in my global JavaScript file. I do the same thing to TinyMCE’s tiny_mce_popup.js file.

    document.domain = 'mysitedomain.com';

(You might also know that cookies need a similar bump when trying to read and write to them across subdomains.)

Although this works, there is a problem for those developing locally: there’s a good chance they’re not developing at mysitedomain.com but something like localhost. A page at localhost certainly isn’t allowed to claim its document domain is mysitedomain.com.

To handle both cases, we can instead set the document domain smartly, by putting this in both our global JavaScript file and in tiny_mce_popup.js:

    document.domain = /(\w+)(.\w+)?$/.exec(location.hostname)[0];