fix: remove empty nodes from serialized server load data (#14404)

* test

* fix

* remove only

* __data.json needs all nodes

* changeset

* lint

Author: PatrickG

.changeset/lazy-boats-stay.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: remove empty nodes from serialized server load data

packages/kit/src/runtime/server/page/data_serializer.js

@@ -1,4 +1,5 @@
 import * as devalue from 'devalue';
+import { compact } from '../../../utils/array.js';
 import { create_async_iterator } from '../../../utils/streaming.js';
 import {
 	clarify_devalue_error,
@@ -96,7 +97,7 @@ export function server_data_serializer(event, event_state, options) {
 			const close = `</script>\n`;
 
 			return {
-				data: `[${strings.join(',')}]`,
+				data: `[${compact(strings).join(',')}]`,
 				chunks: promise_id > 1 ? iterator.iterate((str) => open + str + close) : null
 			};
 		}

packages/kit/src/runtime/server/page/index.js

@@ -195,7 +195,10 @@ export async function render_page(
 						}
 					});
 
-					data_serializer.add_node(i, server_data);
+					if (node) {
+						data_serializer.add_node(i, server_data);
+					}
+
 					data_serializer_json?.add_node(i, server_data);
 
 					return server_data;
@@ -348,7 +351,8 @@ export async function render_page(
 			branch: ssr === false ? [] : compact(branch),
 			action_result,
 			fetched,
-			data_serializer
+			data_serializer:
+				ssr === false ? server_data_serializer(event, event_state, options) : data_serializer
 		});
 	} catch (e) {
 		// if we end up here, it means the data loaded successfully

packages/kit/test/apps/basics/src/routes/load/serialization-empty-node/+error.svelte

@@ -0,0 +1,4 @@
+/** @type {import('./$types').PageServerLoad} */
+export function load() {
+	return { answer: 42 };
+}

packages/kit/test/apps/basics/src/routes/load/serialization-empty-node/+page.server.js

@@ -0,0 +1,6 @@
+<script>
+	/** @type {import('./$types').PageData} */
+	export let data;
+</script>
+
+<h1>{data.answer}</h1>

packages/kit/test/apps/basics/src/routes/load/serialization-empty-node/+page.svelte

@@ -246,6 +246,11 @@ test.describe('Load', () => {
 		);
 	});
 
+	test('Server data serialization removes empty nodes', async ({ page }) => {
+		await page.goto('/load/serialization-empty-node');
+		expect(await page.textContent('h1')).toBe('42');
+	});
+
 	test('POST fetches are serialized', async ({ page, javaScriptEnabled }) => {
 		/** @type {string[]} */
 		const requests = [];