The Modern Web

Polyfills and Shims

A shim (sometimes called a shiv) is a piece of code that intercepts an API call and provides a layer of abstraction, and a polyfill is a specific type of shim that adds support for new or experimental features in browsers that don’t support them natively. CSS multi-columns aren’t supported in many older browsers, for example, so a multi-column polyfill would use JavaScript to replicate their functionality in those browsers.

The idea behind a polyfill is that it happens invisibly; other than including a link to the polyfill file, no (or very little) more should be required from the author. In the case of multi-columns, the CSS to create the columns should be all you need. Of course, multi-columns create a dependency on JavaScript ...