---
title: Polyfill.io
category: JavaScript libraries
updated: 2018-08-20
intro: |
[Polyfill.io](https://polyfill.io) is a service that serves JavaScript polyfills.
---
## Usage
### Default usage
```html
```
{: .-wrap}
This is the default script for Polyfill.io.
### References
* [API example](https://polyfill.io/v2/docs/api) _(polyfill.io)_
* [List of features](https://polyfill.io/v2/docs/features) _(polyfill.io)_
## Optimized
### For modern browsers
```html
```
This only includes polyfill.io when necessary, skipping it for modern browsers for faster load times.
### Extra features
```html
```
This is the same as the previous, but also adds a polyfill for `window.fetch()`. We add a `window.fetch` check and loads the additional `fetch` feature.