Web developers, bless their hearts, feel uncomfortable with the word "emulate", so they use "polyfill", or sometimes the more general "shim". To some degree, "

Web developers, bless their hearts, feel uncomfortable with the word "emulate", so they use "polyfill", or sometimes the more general "shim". To some degree, "polyfill" implies that the functionality being emulated/shimmed is functionality that is under some other circumstances is expected to be provided by the browser itself.