breaking: conditional ActionReturn type if Parameter is void

src/runtime/action/index.ts

@@ -17,26 +17,35 @@
  *
  * Docs: https://svelte.dev/docs#template-syntax-element-directives-use-action
  */
-export interface ActionReturn<Parameter = any> {
-	update?: (parameter: Parameter) => void;
-	destroy?: () => void;
-}
+export type ActionReturn<Parameter = any> = void extends Parameter
+	? {
+		destroy?: () => void;
+	}
+	: {
+		update?: (parameter: Parameter) => void;
+		destroy?: () => void;
+	}
 
 /**
  * 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 }> = (node, param = { someProperty: true }) => {
+ * export const myAction: Action<HTMLDivElement, undefined | { someProperty: boolean }> = (node, param = { someProperty: true }) => {
  *   // ...
  * }
  * ```
- * You can return an object with methods `update` and `destroy` from the function.
+ * If your action doesn't accept a parameter, type if as `Action<HTMLElement, void>`.
+ *
+ * You can return an object with methods `update` (if the action accepts a parameter) and `destroy` from the function.
  * See interface `ActionReturn` for more details.
  *
  * Docs: https://svelte.dev/docs#template-syntax-element-directives-use-action
  */
-export interface Action<Element = HTMLElement, Parameter = any> {
-	<Node extends Element>(node: Node, parameter?: Parameter): void | ActionReturn<Parameter>;
-}
+export type Action<Element = HTMLElement, Parameter = any> = 
+	void extends Parameter
+	? <Node extends Element>(node: Node) => void | ActionReturn<Parameter>
+	: undefined extends Parameter
+	? <Node extends Element>(node: Node, parameter?: Parameter) => void | ActionReturn<Parameter>
+	: <Node extends Element>(node: Node, parameter: Parameter) => void | ActionReturn<Parameter>;