chore: improve the performance of set_text for single expressions (#12893)

Author: trueadm

.changeset/hip-jeans-provide.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: improve the performance of set_text for single expressions

packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js

@@ -64,6 +64,10 @@ export function build_template_literal(values, visit, state) {
 					)
 				);
 				expressions.push(b.call('$.get', id));
+			} else if (values.length === 1) {
+				// If we have a single expression, then pass that in directly to possibly avoid doing
+				// extra work in the template_effect (instead we do the work in set_text).
+				return { value: visit(node.expression, state), has_state, has_call };
 			} else {
 				expressions.push(b.logical('??', visit(node.expression, state), b.literal('')));
 			}

packages/svelte/src/internal/client/render.js

@@ -51,7 +51,8 @@ export function set_text(text, value) {
 	// @ts-expect-error
 	if (value !== (text.__t ??= text.nodeValue)) {
 		// @ts-expect-error
-		text.nodeValue = text.__t = value;
+		text.__t = value;
+		text.nodeValue = value == null ? '' : value + '';
 	}
 }
 

packages/svelte/tests/migrate/samples/each-block-const/output.svelte

@@ -2,4 +2,4 @@
 	const { foo } = x();
 </script>
 
-{#each foo as f}{/each}
+{#each foo as f}{/each}

packages/svelte/tests/snapshot/samples/purity/_expected/client/index.svelte.js

@@ -11,11 +11,11 @@ export default function Purity($$anchor) {
 	var fragment = root();
 	var p = $.first_child(fragment);
 
-	p.textContent = `${Math.max(min, Math.min(max, number)) ?? ""}`;
+	p.textContent = Math.max(min, Math.min(max, number));
 
 	var p_1 = $.sibling($.sibling(p, true));
 
-	p_1.textContent = `${location.href ?? ""}`;
+	p_1.textContent = location.href;
 
 	var node = $.sibling($.sibling(p_1, true));