Treehouse

Detect Pseudo-Element Animation Support

By on  

A while back I posted an interesting tidbit from Daniel Buchner which allows developers to detect DOM node insertions with JavaScript and CSS animations; an awesome trick driven by CSS animations.  Lea Verou recently posted another detection snippet driven by CSS animations:  detecting pseudo-element animation support.  Here's how she did it!

The CSS

The test case can use any pseudo-element; in this case we'll use :before:

/**
 * Animation on pseudo-elements test
 */
@keyframes color { from,to { color: rgb(0, 255, 0); } }

.testElement:before {
	content: '(...testing animation support...)';
	color: rgb(255, 0, 0);
	animation: color 1s infinite;
	-webkit-animation: color 1s infinite;
}

A simple color animation is assigned to the pseudo-element and a spot-check of generated content will tell you if animation is supported (green) or not (red).  At the time of this post, only Firefox and Chrome support animation of psuedo-elements.

JavaScript Detection

Thanks to a tip from Ahmed El Gabri, I can present a method to detect pseudo-element animation:

var color = window.getComputedStyle(
	document.querySelector('.testElement'), ':before'
).getPropertyValue('color')

if(color == 'rgb(0, 255, 0)') {
	// Supported! :)
}

The same principal applies; if the color is green, the animation worked. A JavaScript method of feature detection makes everything better!

Unfortunately there doesn't appear to be a JavaScript method for testing generated content properties, so a spot check appears to be all we can rely on at this point.  Hopefully someone clever out there can figure out an efficient way to get the test result! Having a reliable method for detecting pseudo-element animation is excellent; another tool to add to the arsenal!

ydkjs-2.png

Recent Features

Incredible Demos

  • Flashy FAQs Using MooTools Sliders

    I often qualify a great website by one that pay attention to detail and makes all of the "little things" seem as though much time was spent on them. Let's face it -- FAQs are as boring as they come. That is, until you...

  • WordPress-Style Comment Controls Using MooTools or jQuery

    WordPress has a nice little effect on the Admin Dashboard where it shows and hides the comment control links when you mouseover and mouseout of the record's container. Here's how to achieve that effect using MooTools or jQuery. The XHTML Notice that we place the links into...

Discussion

  1. Actually, Chrome 26 added support for animating psuedo-elements, which was released to stable this week!

  2. I don’t know if this helps but I think you can check generated content properties, try this

    window.getComputedStyle(document.querySelector('.testElement'),':before').getPropertyValue('color'); 
    

    I read about it here http://adactio.com/journal/5429/

  3. Works like a champ in Chrome too!

    Maybe David needs an update ;)

  4. Updated my Chrome and I see green — yay!

  5. Didn’t IE (up to 10) not support the second argument in getComputedStyle() until recently? Did they fix it? I recall somebody reported it and they said it was by design (!).

  6. I have installed chrome online, but still it does not supporting Pseudo-Element. However, my Mozilla is showing green text …

  7. Rob Riggs

    What if I want to change the content property of the psuedo class, by keyframe? Any takers? Thanks!

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!