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Useponyfill.com for linking here.

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

Apolyfill is code that adds missing functionality bymonkey 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??=function(value){returnvalue!==value;};

import'is-nan-polyfill';Number.isNaN(5);

exportdefaultfunctionisNaN(value){returnvalue!==value;};

importisNanPonyfillfrom'is-nan-ponyfill';isNanPonyfill(5);

Ponyfills should avoid using native APIs, because potential bugs or differences in the native APIs will make such a ponyfill less robust (therefore defeating one of its main purposes). There are important exceptions, such as when:

• There is no way to implement some of the ponyfill without native APIs.
• Reimplementing native parts would have a large cost (e.g. performance or code size).

In such cases, it's still valuable for the ponyfill to minimize any assumptions about the underlying environment.

Search npm.

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

• Ponyfill definition - Silicon 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 byMary Winkler.