simpler and removal of the "first" trick

packages/svelte/src/internal/client/dom/template.js

@@ -72,25 +72,8 @@ export function template(content, flags) {
  */
 /*#__NO_SIDE_EFFECTS__*/
 export function template_with_script(content, flags) {
-	var first = true;
-	var fn = template(content, flags | TEMPLATE_FRAGMENT);
-
-	return () => {
-		if (hydrating) return fn();
-
-		var fragment = /** @type {DocumentFragment} */ (fn());
-
-		if (first) {
-			first = false;
-			run_scripts(fragment);
-		}
-
-		if ((flags & TEMPLATE_FRAGMENT) !== 0) {
-			return fragment;
-		}
-
-		return /** @type {Node} */ (fragment.firstChild);
-	};
+	var fn = template(content, flags);
+	return () => run_scripts(/** @type {Element | DocumentFragment} */ (fn()));
 }
 
 /**
@@ -155,25 +138,8 @@ export function ns_template(content, flags, ns = 'svg') {
  */
 /*#__NO_SIDE_EFFECTS__*/
 export function svg_template_with_script(content, flags) {
-	var first = true;
-	var fn = ns_template(content, flags | TEMPLATE_FRAGMENT);
-
-	return () => {
-		if (hydrating) return fn();
-
-		var fragment = /** @type {DocumentFragment} */ (fn());
-
-		if (first) {
-			first = false;
-			run_scripts(fragment);
-		}
-
-		if ((flags & TEMPLATE_FRAGMENT) !== 0) {
-			return fragment;
-		}
-
-		return /** @type {Node} */ (fragment.firstChild);
-	};
+	var fn = ns_template(content, flags);
+	return () => run_scripts(/** @type {Element | DocumentFragment} */ (fn()));
 }
 
 /**
@@ -189,15 +155,21 @@ export function mathml_template(content, flags) {
 /**
  * Creating a document fragment from HTML that contains script tags will not execute
  * the scripts. We need to replace the script tags with new ones so that they are executed.
- * @param {DocumentFragment} fragment
+ * @param {Element | DocumentFragment} node
+ * @returns {Node | Node[]}
  */
-function run_scripts(fragment) {
+function run_scripts(node) {
 	// scripts were SSR'd, in which case they will run
-	if (hydrating) return;
+	if (hydrating) return node;
 
+	const is_fragment = node.nodeType === 11;
+	const scripts =
+		/** @type {HTMLElement} */ (node).tagName === 'SCRIPT'
+			? [/** @type {HTMLScriptElement} */ (node)]
+			: node.querySelectorAll('script');
 	const effect = /** @type {Effect} */ (active_effect);
 
-	for (const script of fragment.querySelectorAll('script')) {
+	for (const script of scripts) {
 		const clone = document.createElement('script');
 		for (var attribute of script.attributes) {
 			clone.setAttribute(attribute.name, attribute.value);
@@ -206,15 +178,22 @@ function run_scripts(fragment) {
 		clone.textContent = script.textContent;
 
 		// The script has changed - if it's at the edges, the effect now points at dead nodes
-		if (fragment.firstChild === script) {
+		if (is_fragment ? node.firstChild === script : node === script) {
 			effect.nodes_start = clone;
 		}
-		if (fragment.lastChild === script) {
+		if (is_fragment ? node.lastChild === script : node === script) {
 			effect.nodes_end = clone;
 		}
 
-		script.replaceWith(clone);
+		// If node === script tag, replaceWith will do nothing because there's no parent yet
+		if (script === node) {
+			// but we can returns the cloned <script> immediately
+			return clone;
+		} else {
+			script.replaceWith(clone);
+		}
 	}
+	return node;
 }
 
 /**