For example, a polyfill could be used to mimic the functionality of an HTML Canvas element on Microsoft Internet Explorer 7 using a Silverlight plugin or mimic support for CSS rem units, or
text-shadow, or whatever you want.
The reason why polyfills are not used exclusively is for better functionality and better performance. Native implementations of APIs can do more and are faster than polyfills. For example, the Object.create polyfill only contains the functionalities that are possible in a non-native implementation of Object.create.
- What is a polyfill? (article by Remy Sharp, the originator of the term)