parameter Class — svelte Architecture

Source Code

packages/svelte/types/index.d.ts lines 604–676

declare module 'svelte/action' {
	/**
	 * 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<undefined>` 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<boolean>) => void;
	 * }
	 *
	 * export function myAction(node: HTMLElement, parameter: Parameter): ActionReturn<Parameter, Attributes> {
	 * 	// ...
	 * 	return {
	 * 		update: (updatedParameter) => {...},
	 * 		destroy: () => {...}
	 * 	};
	 * }
	 * ```
	 */
	export interface ActionReturn<
		Parameter = undefined,
		Attributes extends Record<string, any> = Record<never, any>
	> {
		update?: (parameter: Parameter) => void;
		destroy?: () => void;
		/**
		 * ### DO NOT USE THIS
		 * This exists solely for type-checking and has no effect at runtime.
		 * Set this through the `Attributes` generic instead.
		 */
		$$_attributes?: Attributes;
	}

	/**
	 * 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 `<div>` elements
	 * and optionally accepts a parameter which it has a default value for:
	 * ```ts
	 * export const myAction: Action<HTMLDivElement, { someProperty: boolean } | undefined> = (node, param = { someProperty: true }) => {
	 *   // ...
	 * }
	 * ```
	 * `Action<HTMLDivElement>` and `Action<HTMLDivElement, undefined>` 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.
	 */
	export interface Action<
		Element = HTMLElement,
		Parameter = undefined,
		Attributes extends Record<string, any> = Record<never, any>
	> {
		<Node extends Element>(
			...args: undefined extends Parameter
				? [node: Node, parameter?: Parameter]
				: [node: Node, parameter: Parameter]
		): void | ActionReturn<Parameter, Attributes>;
	}

	// Implementation notes:
	// - undefined extends X instead of X extends undefined makes this work better with both strict and nonstrict mode

	export {};
}