# svelte/attachments

```js
// @noErrors
import { createAttachmentKey, fromAction } from 'svelte/attachments';
```

## createAttachmentKey

<blockquote class="since note">

Available since 5.29

</blockquote>

Creates an object key that will be recognised as an attachment when the object is spread onto an element,
as a programmatic alternative to using `{@attach ...}`. This can be useful for library authors, though
is generally not needed when building an app.

```svelte
<script>
	import { createAttachmentKey } from 'svelte/attachments';

	const props = {
		class: 'cool',
		onclick: () => alert('clicked'),
		[createAttachmentKey()]: (node) => {
			node.textContent = 'attached!';
		}
	};
</script>

<button {...props}>click me</button>
```

<div class="ts-block">

```dts
function createAttachmentKey(): symbol;
```

</div>



## fromAction

Converts an [action](/docs/svelte/use) into an [attachment](/docs/svelte/@attach) keeping the same behavior.
It's useful if you want to start using attachments on components but you have actions provided by a library.

Note that the second argument, if provided, must be a function that _returns_ the argument to the
action function, not the argument itself.

```svelte
<!-- with an action -->
<div use:foo={bar}>...</div>

<!-- with an attachment -->
<div {@attach fromAction(foo, () => bar)}>...</div>
```

<div class="ts-block">

```dts
function fromAction<
	E extends EventTarget,
	T extends unknown
>(
	action:
		| Action<E, T>
		| ((element: E, arg: T) => void | ActionReturn<T>),
	fn: () => T
): Attachment<E>;
```

</div>

<div class="ts-block">

```dts
function fromAction<E extends EventTarget>(
	action:
		| Action<E, void>
		| ((element: E) => void | ActionReturn<void>)
): Attachment<E>;
```

</div>



## Attachment

An [attachment](/docs/svelte/@attach) is a function that runs when an element is mounted
to the DOM, and optionally returns a function that is called when the element is later removed.

It can be attached to an element with an `{@attach ...}` tag, or by spreading an object containing
a property created with [`createAttachmentKey`](/docs/svelte/svelte-attachments#createAttachmentKey).

<div class="ts-block">

```dts
interface Attachment<T extends EventTarget = Element> {/*…*/}
```

<div class="ts-block-property">

```dts
(element: T): void | (() => void);
```

<div class="ts-block-property-details"></div>
</div></div>