I recently added to my growing library of image-preloading methods with a few new-&-improved techniques. After posting that recent preloading article, an even better way of preloading images using pure CSS3 hit me:

.preload-images {
	background: url(image-01.png) no-repeat -9999px -9999px;
	background: url(image-01.png) no-repeat -9999px -9999px,
		    url(image-02.png) no-repeat -9999px -9999px,
		    url(image-03.png) no-repeat -9999px -9999px,
		    url(image-04.png) no-repeat -9999px -9999px,
		    url(image-05.png) no-repeat -9999px -9999px;
	}

Using CSS3’s new support for multiple background images, we can use a single, existing element to preload all of the required images. Compare this method with the old way of using CSS to preload images:

.preload-01 { background: url(image-01.png) no-repeat -9999px -9999px; }  
.preload-02 { background: url(image-02.png) no-repeat -9999px -9999px; }  
.preload-03 { background: url(image-03.png) no-repeat -9999px -9999px; }
.preload-04 { background: url(image-04.png) no-repeat -9999px -9999px; }
.preload-05 { background: url(image-05.png) no-repeat -9999px -9999px; }

As you can see, the CSS3 method is a much cleaner way to preload your images using a single CSS selector. Note that we’re also going to need to ensure the background images aren’t being displayed in the preload element. For that, I suppose we could either hide the element using display:none or else position the images far off screen using -9999px positioning.

Pros

This technique works great in supportive browsers now, and the support will only get better moving into the future. Notice that we can include a partial fallback mechanism by preloading one of the images as a single background property value. Browsers that don’t get the multiple stuff will fallback to the single-value background property instead.

Also, browser support for CSS is much better than for JavaScript, so big improvement there. Beyond these things, the sheer ease of picking an element and adding all of our preload images as backgrounds is simply too easy not to take advantage.

Cons

Well, let’s see.. current browser support is not as good as it could be, mostly because of Internet Explorer. So besides the fact that IE may never understand multiple background-images, the downsides to using this method are pretty much nil as far as I can tell. Perhaps I am missing something completely obvious..? Maybe someone will elaborate on the non-presentational use of CSS? ;) Chime in!