> For the complete documentation index, see [llms.txt](https://bryan-guner.gitbook.io/duke/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://bryan-guner.gitbook.io/duke/most-useful/react/javascript-environment-requirements.md).

# JavaScript Environment Requirements

React 16 depends on the collection types [Map](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) and [Set](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set). If you support older browsers and devices which may not yet provide these natively (e.g. IE < 11) or which have non-compliant implementations (e.g. IE 11), consider including a global polyfill in your bundled application, such as [core-js](https://github.com/zloirock/core-js).

A polyfilled environment for React 16 using core-js to support older browsers might look like:

```js
import "core-js/es/map";
import "core-js/es/set";

import React from "react";
import ReactDOM from "react-dom";

ReactDOM.render(<h1>Hello, world!</h1>, document.getElementById("root"));
```

React also depends on `requestAnimationFrame` (even in test environments).\
You can use the [raf](https://www.npmjs.com/package/raf) package to shim `requestAnimationFrame`:

```js
import "raf/polyfill";
```