From f67d03df5b49e7c9c2e65ec66739f30c9d3d403a Mon Sep 17 00:00:00 2001
From: Paolo Ricciuti <ricciutipaolo@gmail.com>
Date: Sun, 22 Feb 2026 14:40:49 +0100
Subject: [PATCH] fix: make string coercion consistent to `toString` (#17774)

Closes #17758

### Before submitting the PR, please make sure you do the following

- [x] It's really useful if your PR references an issue where it is
discussed ahead of time. In many cases, features are absent for a
reason. For large changes, please create an RFC:
https://github.com/sveltejs/rfcs
- [x] Prefix your PR title with `feat:`, `fix:`, `chore:`, or `docs:`.
- [x] This message body should clearly illustrate what problems it
solves.
- [x] Ideally, include a test that fails without this PR but passes with
it.
- [x] If this PR changes code within `packages/svelte/src`, add a
changeset (`npx changeset`).

### Tests and linting

- [x] Run the tests with `pnpm test` and lint the project with `pnpm
lint`
---
 .changeset/thirty-groups-rhyme.md             |  5 +++++
 packages/svelte/src/internal/client/render.js |  4 ++--
 .../set-text-stable-coercion/_config.js       |  6 +++++
 .../set-text-stable-coercion/main.svelte      | 22 +++++++++++++++++++
 4 files changed, 35 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/thirty-groups-rhyme.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/set-text-stable-coercion/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/set-text-stable-coercion/main.svelte

diff --git a/.changeset/thirty-groups-rhyme.md b/.changeset/thirty-groups-rhyme.md
new file mode 100644
index 0000000000..5a6bde7677
--- /dev/null
+++ b/.changeset/thirty-groups-rhyme.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: make string coercion consistent to `toString`
diff --git a/packages/svelte/src/internal/client/render.js b/packages/svelte/src/internal/client/render.js
index 4316403ba6..cb152ed9c1 100644
--- a/packages/svelte/src/internal/client/render.js
+++ b/packages/svelte/src/internal/client/render.js
@@ -45,12 +45,12 @@ export function set_should_intro(value) {
  */
 export function set_text(text, value) {
 	// For objects, we apply string coercion (which might make things like $state array references in the template reactive) before diffing
-	var str = value == null ? '' : typeof value === 'object' ? value + '' : value;
+	var str = value == null ? '' : typeof value === 'object' ? `${value}` : value;
 	// @ts-expect-error
 	if (str !== (text.__t ??= text.nodeValue)) {
 		// @ts-expect-error
 		text.__t = str;
-		text.nodeValue = str + '';
+		text.nodeValue = `${str}`;
 	}
 }
 
diff --git a/packages/svelte/tests/runtime-runes/samples/set-text-stable-coercion/_config.js b/packages/svelte/tests/runtime-runes/samples/set-text-stable-coercion/_config.js
new file mode 100644
index 0000000000..01ef02510a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/set-text-stable-coercion/_config.js
@@ -0,0 +1,6 @@
+import { test } from '../../test';
+
+export default test({
+	html: 'toString <p>toString</p> <p>[toString]</p> toString',
+	async test() {}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/set-text-stable-coercion/main.svelte b/packages/svelte/tests/runtime-runes/samples/set-text-stable-coercion/main.svelte
new file mode 100644
index 0000000000..601e7ce9fb
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/set-text-stable-coercion/main.svelte
@@ -0,0 +1,22 @@
+<script>
+	class Widget {
+		toString() { return "toString" }
+		valueOf() { return "valueOf" }
+	}
+
+	const value = new Widget();
+</script>
+
+<!-- case 1 -->
+{value}
+
+<!-- case 2 -->
+<p>{value}</p>
+
+<!-- case 3 -->
+<p>[{value}]</p>
+
+<!-- case 4 -->
+{#if 1}
+	{value}
+{/if}