Yepnope.js Allows HTML5 and CSS3 With Graceful Degradation
Many smart web developers use tools such as Modernizr to detect browser features with graceful degradation, but why not test and load polyfills at the same time? That's what you can do using the Yepnope.js asynchronous conditional resource loader.
For those who don't know what the term "polyfill" refers to, it is a snippet of code (or plug-in) that fills in for technology that is absent, such as some of the features of HTML5 or CSS3, in this instance.
The folks who created Modernizr think that Yepnope.js is a great concept--so much so that they are integrating it into the next version, called appropriately Modernizr 2. Yepnope.js only adds 1.6 kilobytes to your web page, so it won't slow your visitors down, and may in fact speed up page loading time.