Use ponyfill.com for linking here.

While polyfills are naughty, ponyfills are pure, just like ponies.

A polyfill is code that adds missing functionality by monkey patching an API. Unfortunately, it usually globally patches built-ins, which affects all code running in the environment. This is especially problematic when a polyfill is not fully spec compliant (which in some cases is impossible), as it could cause very hard to debug bugs and inconsistencies. Or when the spec for a new feature changes and your code depends on behavior that a module somewhere else in the dependency tree polyfills differently. In general, you should not modify API's you don't own.

A ponyfill, in contrast, doesn't monkey patch anything, but instead exports the functionality as a normal module, so you can use it locally without affecting other code.

tl;dr; Polyfills are naughty as they patch native APIs, while ponyfills are pure and don't affect the environment.

Number.isNaN = Number.isNaN || function (value) {
	return value !== value;
};

require('is-nan-polyfill');

Number.isNaN(5);

module.exports = function (value) {
	return value !== value;
};

var isNanPonyfill = require('is-nan-ponyfill');

isNanPonyfill(5);

Ponyfills should never use the native API, even if available, as it might have slightly different behavior between environments, which can cause bugs.

Search npm.

• Read the specification or source code of the feature you want ponyfill.
• Initialize an npm package.
• Write some tests to ease writing the ponyfill logic.
• Link to documentation about the feature in your readme. Example.
• Link to https://ponyfill.com in your readme. Example.
• Add ponyfill to the keywords section in package.json.
• Publish!

• Ponyfill definition - Sillicon Valley Dictionary
• Polyfills or Ponyfills? - Pony Foo
• Polyfill, Ponyfill and Prollyfill - Kikobeats

To the extent possible under law, Sindre Sorhus has waived all copyright and related or neighboring rights to this work.

Header based on work by Mary Winkler.