When using CSS, we can just include both declarations, one using rgba, and one without it, as mentioned in my post on cross-browser RGBA backgrounds. When writing JavaScript however, it’s a waste of resources to do that (and requires more verbose code), since we can easily check whether the browser is RGBA-capable, almost as easily as we can check whether it suppports a given property. We can even follow the same technique to detect the support of other CSS3 values (for instance, multiple b...
