From 6614dca13687ebd254502074c01d9a12428ada73 Mon Sep 17 00:00:00 2001
From: Bao Nguyen <waycaosi1994@gmail.com>
Date: Fri, 4 Sep 2026 14:03:36 +0700
Subject: [PATCH] fix: serialize `<textarea>` default values during server
 rendering

---
 .changeset/heavy-pandas-shout.md              |  5 ++++
 .../server/visitors/shared/element.js         | 24 +++++++++++++++++++
 .../samples/textarea-default-value/_config.js |  3 +++
 .../textarea-default-value/_expected.html     |  4 ++++
 .../textarea-default-value/main.svelte        |  8 +++++++
 5 files changed, 44 insertions(+)
 create mode 100644 .changeset/heavy-pandas-shout.md
 create mode 100644 packages/svelte/tests/server-side-rendering/samples/textarea-default-value/_config.js
 create mode 100644 packages/svelte/tests/server-side-rendering/samples/textarea-default-value/_expected.html
 create mode 100644 packages/svelte/tests/server-side-rendering/samples/textarea-default-value/main.svelte

diff --git a/.changeset/heavy-pandas-shout.md b/.changeset/heavy-pandas-shout.md
new file mode 100644
index 0000000000..54d2dc28e5
--- /dev/null
+++ b/.changeset/heavy-pandas-shout.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: serialize `<textarea>` default values during server rendering
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/element.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/element.js
index c19d760f48..fa8a555d32 100644
--- a/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/element.js
+++ b/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/element.js
@@ -88,6 +88,13 @@ export function build_element_attributes(node, context, transform) {
 				attributes.push(attribute);
 				// deopt to spread at runtime, where we can handle interaction of value/defaultValue etc
 				has_spread = true;
+			} else if (
+				node.type === 'RegularElement' &&
+				node.name === 'textarea' &&
+				attribute.name === 'defaultValue' &&
+				renders_default_value_as_content(node)
+			) {
+				content = b.call('$.escape', build_attribute_value(attribute.value, context, transform));
 				// the defaultValue/defaultChecked properties don't exist as attributes
 			} else if (attribute.name !== 'defaultValue' && attribute.name !== 'defaultChecked') {
 				if (attribute.name === 'class') {
@@ -293,6 +300,23 @@ export function build_element_attributes(node, context, transform) {
 	return content;
 }
 
+/**
+ * A `<textarea>` has no value attribute, so `defaultValue` can only be serialized as its content,
+ * which is possible when nothing else already provides one.
+ * @param {AST.RegularElement} node
+ */
+function renders_default_value_as_content(node) {
+	return (
+		node.fragment.nodes.length === 0 &&
+		!node.attributes.some(
+			(attribute) =>
+				attribute.type === 'SpreadAttribute' ||
+				((attribute.type === 'Attribute' || attribute.type === 'BindDirective') &&
+					attribute.name === 'value')
+		)
+	);
+}
+
 /**
  * @param {AST.RegularElement | AST.SvelteElement} element
  * @param {AST.Attribute | AST.BindDirective} attribute
diff --git a/packages/svelte/tests/server-side-rendering/samples/textarea-default-value/_config.js b/packages/svelte/tests/server-side-rendering/samples/textarea-default-value/_config.js
new file mode 100644
index 0000000000..f47bee71df
--- /dev/null
+++ b/packages/svelte/tests/server-side-rendering/samples/textarea-default-value/_config.js
@@ -0,0 +1,3 @@
+import { test } from '../../test';
+
+export default test({});
diff --git a/packages/svelte/tests/server-side-rendering/samples/textarea-default-value/_expected.html b/packages/svelte/tests/server-side-rendering/samples/textarea-default-value/_expected.html
new file mode 100644
index 0000000000..e2f88f6b01
--- /dev/null
+++ b/packages/svelte/tests/server-side-rendering/samples/textarea-default-value/_expected.html
@@ -0,0 +1,4 @@
+<textarea>hello</textarea>
+<textarea>world</textarea>
+<textarea>content wins</textarea>
+<textarea>value wins</textarea>
diff --git a/packages/svelte/tests/server-side-rendering/samples/textarea-default-value/main.svelte b/packages/svelte/tests/server-side-rendering/samples/textarea-default-value/main.svelte
new file mode 100644
index 0000000000..5b7a41c368
--- /dev/null
+++ b/packages/svelte/tests/server-side-rendering/samples/textarea-default-value/main.svelte
@@ -0,0 +1,8 @@
+<script>
+	let dynamic = 'world';
+</script>
+
+<textarea defaultValue="hello"></textarea>
+<textarea defaultValue={dynamic}></textarea>
+<textarea defaultValue="hello">content wins</textarea>
+<textarea defaultValue="hello" value="value wins"></textarea>