Sunday, November 27, 2016

What is Polyfill as related to JavaScript?

In the early days of Internet (some 10 years ago or so) one had to write some kind of code that recognizes the browser and control the flow so that the audience is given the information that there was no browser support for the functionality.

An extreme kind of instruction was that the browser's JavaScript functionality was not on, etc.

A Polyfill ( piece of code, plug-in,add-in, script) is a browser fallback so that feature(s) works in a modern browser also works in older browsers which per se did not support what is supported in the modern browser.

Here is a comprehensive collection of HTML5 Cross Browser Polyfills.

The term Polyfills was coined by Remy Sharp to describe JavaScript shims that replicate standard API found in modern browsers for those older browsers that do not support.

Polyfills are created by developers to fulfill this requirement and one can create ones own Polyfill .

One of the most popular Polyfills is htmlshiv (

In IE versions of 9.0 and prior versions
and would have been parsed as empty elements. These tags however described nesting of elements and styling them would have been difficult. Html5shiv takes care of this by directing the page if opened in IE 9 to use the appropriate script:

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