• Code that implements a feature on web browsers that do not natively support the feature. Most often, a polyfill refers to a JavaScript library that implements an HTML web standard, either an established one (supported by some browsers) on older browsers, or a proposed standard (not supported by any browsers) on existing browsers. Formally, a polyfill is a shim for a browser API. Polyfills allow web developers to use an API regardless of whether it is supported by a browser, and usually with minimal overhead. ← Wikipedia

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