simplify implementation - create action first, then only create update/destroy effects if necessary

packages/svelte/src/attachments/index.js

@@ -1,9 +1,8 @@
-/**
- * @import { FromAction } from "./public.js";
- * @import { ActionReturn } from "svelte/action";
- */
-import { render_effect } from 'svelte/internal/client';
+/** @import { FromAction } from './public.js' */
+import { noop, render_effect } from 'svelte/internal/client';
 import { ATTACHMENT_KEY } from '../constants.js';
+import { untrack } from 'svelte';
+import { teardown } from '../internal/client/reactivity/effects.js';
 
 /**
  * Creates an object key that will be recognised as an attachment when the object is spread onto an element,
@@ -36,36 +35,21 @@ export function createAttachmentKey() {
  * attachments on Components but you have library provided actions.
  * @type {FromAction}
  */
-export function fromAction(action, args) {
+export function fromAction(action, /** @type {() => any} */ get_arg = noop) {
 	return (element) => {
-		/**
-		 * @typedef {typeof args} Args;
-		 */
+		const { update, destroy } = untrack(() => action(element, get_arg()) ?? {});
 
-		/**
-		 * @type {ReturnType<NonNullable<Args>> | undefined}
-		 */
-		let actual_args;
-		/**
-		 * @type {ActionReturn['update']}
-		 */
-		let update;
-		/**
-		 * @type {ActionReturn['destroy']}
-		 */
-		let destroy;
+		if (update) {
+			var ran = false;
 			render_effect(() => {
-			actual_args = args?.();
-			update?.(/** @type {any} */ (actual_args));
+				const arg = get_arg();
+				if (ran) update(arg);
 			});
+			ran = true;
+		}
 
-		render_effect(() => {
-			return () => {
-				destroy?.();
-			};
-		});
-		({ update, destroy } = /** @type {ActionReturn} */ (
-			action(element, /** @type {any} */ (actual_args))
-		));
+		if (destroy) {
+			teardown(destroy);
+		}
 	};
 }