--- NOTE: do not edit this file, it is generated in apps/svelte.dev/scripts/sync-docs/index.ts title: svelte/action --- This module provides types for [actions](use), which have been superseded by [attachments](@attach). ## Action Actions are functions that are called when an element is created. You can use this interface to type such actions. The following example defines an action that only works on `

` elements and optionally accepts a parameter which it has a default value for: ```ts export const myAction: Action = (node, param = { someProperty: true }) => { // ... } ``` `Action` and `Action` both signal that the action accepts no parameters. You can return an object with methods `update` and `destroy` from the function and type which additional attributes and events it has. See interface `ActionReturn` for more details.

```dts interface Action< Element = HTMLElement, Parameter = undefined, Attributes extends Record = Record< never, any > > {/*…*/} ```

```dts ( ...args: undefined extends Parameter ? [node: Node, parameter?: Parameter] : [node: Node, parameter: Parameter] ): void | ActionReturn; ```

## ActionReturn Actions can return an object containing the two properties defined in this interface. Both are optional. - update: An action can have a parameter. This method will be called whenever that parameter changes, immediately after Svelte has applied updates to the markup. `ActionReturn` and `ActionReturn` both mean that the action accepts no parameters. - destroy: Method that is called after the element is unmounted Additionally, you can specify which additional attributes and events the action enables on the applied element. This applies to TypeScript typings only and has no effect at runtime. Example usage: ```ts interface Attributes { newprop?: string; 'on:event': (e: CustomEvent) => void; } export function myAction(node: HTMLElement, parameter: Parameter): ActionReturn { // ... return { update: (updatedParameter) => {...}, destroy: () => {...} }; } ```

```dts interface ActionReturn< Parameter = undefined, Attributes extends Record = Record< never, any > > {/*…*/} ```

```dts update?: (parameter: Parameter) => void; ```

```dts destroy?: () => void; ```