# Token List
Constructable, plain JavaScript [DOMTokenList](https://developer.mozilla.org/en-US/docs/Web/API/DOMTokenList) implementation, supporting non-browser runtimes.
## Installation
Install the module
```bash
npm install @wordpress/token-list
```
_This package assumes that your code will run in an **ES2015+** environment. If you're using an environment that has limited or no support for such language features and APIs, you should include [the polyfill shipped in `@wordpress/babel-preset-default`](https://github.com/WordPress/gutenberg/tree/HEAD/packages/babel-preset-default#polyfill) in your code._
## Usage
Construct a new token list, optionally with an initial value. A value with an interface matching DOMTokenList is returned.
```js
import TokenList from '@wordpress/token-list';
const tokens = new TokenList( 'abc def' );
tokens.add( 'ghi' );
tokens.remove( 'def' );
tokens.replace( 'abc', 'xyz' );
console.log( tokens.value );
// "xyz ghi"
```
All [methods of DOMTokenList](https://developer.mozilla.org/en-US/docs/Web/API/DOMTokenList#Methods) are implemented.
Note the following implementation divergences from the [specification](https://dom.spec.whatwg.org/#domtokenlist):
- `TokenList#supports` will always return true, regardless of the token passed.
- `TokenList#add` and `TokenList#remove` will simply disregard the empty string argument or whitespace of a token argument, rather than [throwing an error](https://dom.spec.whatwg.org/#dom-domtokenlist-add).
- An item cannot be referenced by its index as a property. Use `TokenList#item` instead.
## Browser Support
While it could be used in one's implementation, this is not intended to serve as a polyfill for `Element#classList` or other instances of `DOMTokenList`.
The implementation of the `DOMTokenList` interface provided through `@wordpress/token-list` is broadly compatible in environments supporting ES5 (IE8 and newer). That being said, due to its internal implementation leveraging arrays for `TokenList#entries`, `TokenList#forEach`, `TokenList#keys`, and `TokenList#values`, you may need to assure that these functions are supported or polyfilled if you intend to use them.
- https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/entries#Browser_compatibility
- https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/values#Browser_compatibility
TokenList's own internal implementation of the `DOMTokenList` interface does not leverage any of these functions, so it is not necessary to polyfill them for basic usage.
## Contributing to this package
This is an individual package that's part of the Gutenberg project. The project is organized as a monorepo. It's made up of multiple self-contained software packages, each with a specific purpose. The packages in this monorepo are published to [npm](https://www.npmjs.com/) and used by [WordPress](https://make.wordpress.org/core/) as well as other software projects.
To find out more about contributing to this package or Gutenberg as a whole, please read the project's main [contributor guide](https://github.com/WordPress/gutenberg/tree/HEAD/CONTRIBUTING.md).
