---
title: Attributes.add()
---

The `Attributes.add()` method adds `value` to the attribute identified by
`key`.

## Signature

```js
Attributes attributes.add(string key, string value)
```

## Example

```js
const attr = new Attributes()
  .add('class', 'classA')
  .add('class', 'classB')
```

## Notes

Adding multiple values to the same key will result in them being joined together
(with a space) when rendering.