From dd148f6956a9bcddd562c10a388023bad3ff391a Mon Sep 17 00:00:00 2001
From: Matth <42407879+TheSpeedM@users.noreply.github.com>
Date: Tue, 7 Jan 2025 19:49:04 +0100
Subject: [PATCH 1/3] fix: Make Tween duration 0 set current to target
 immediately

---
 .changeset/cold-cups-act.md           |  5 +++++
 packages/svelte/src/motion/tweened.js |  9 +++++++++
 packages/svelte/tests/motion/test.ts  | 18 +++++++++++++++++-
 3 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/cold-cups-act.md

diff --git a/.changeset/cold-cups-act.md b/.changeset/cold-cups-act.md
new file mode 100644
index 000000000000..6776d4eef352
--- /dev/null
+++ b/.changeset/cold-cups-act.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: Make Tween duration 0 set current to target immediately
diff --git a/packages/svelte/src/motion/tweened.js b/packages/svelte/src/motion/tweened.js
index 8aaefe5a2caf..62958a05e76e 100644
--- a/packages/svelte/src/motion/tweened.js
+++ b/packages/svelte/src/motion/tweened.js
@@ -240,6 +240,15 @@ export class Tween {
 			interpolate = get_interpolator
 		} = { ...this.#defaults, ...options };
 
+		if (duration === 0) {
+			if (previous_task) {
+				previous_task.abort();
+				previous_task = null;
+			}
+			set(this.#current, value);
+			return Promise.resolve();
+		}
+
 		const start = raf.now() + delay;
 
 		/** @type {(t: number) => T} */
diff --git a/packages/svelte/tests/motion/test.ts b/packages/svelte/tests/motion/test.ts
index b6554e5e56ed..50606cbb86e2 100644
--- a/packages/svelte/tests/motion/test.ts
+++ b/packages/svelte/tests/motion/test.ts
@@ -2,7 +2,7 @@
 import '../helpers.js'; // for the matchMedia polyfill
 import { describe, it, assert } from 'vitest';
 import { get } from 'svelte/store';
-import { spring, tweened } from 'svelte/motion';
+import { spring, tweened, Tween } from 'svelte/motion';
 
 describe('motion', () => {
 	describe('spring', () => {
@@ -39,4 +39,20 @@ describe('motion', () => {
 			assert.equal(get(size), 20);
 		});
 	});
+
+	describe('Tween', () => {
+		it('sets immediately when duration is 0', () => {
+			const size = new Tween(0);
+
+			size.set(100, { duration: 0 });
+			assert.equal(size.current, 100);
+		})
+	});
+
+	it('updates correctly when initialized with a `null`-ish value', () => {
+		const size = new Tween(undefined as unknown as number, { duration: 0 });
+
+		size.set(10);
+		assert.equal(size.current, 10);
+	});
 });

From 862677749be1e95c3abec40dfacc2bb1911773f7 Mon Sep 17 00:00:00 2001
From: Matth <42407879+TheSpeedM@users.noreply.github.com>
Date: Tue, 7 Jan 2025 20:02:01 +0100
Subject: [PATCH 2/3] Run prettier on test file

---
 packages/svelte/tests/motion/test.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/svelte/tests/motion/test.ts b/packages/svelte/tests/motion/test.ts
index 50606cbb86e2..7d845bac3d05 100644
--- a/packages/svelte/tests/motion/test.ts
+++ b/packages/svelte/tests/motion/test.ts
@@ -46,7 +46,7 @@ describe('motion', () => {
 
 			size.set(100, { duration: 0 });
 			assert.equal(size.current, 100);
-		})
+		});
 	});
 
 	it('updates correctly when initialized with a `null`-ish value', () => {

From f47ab966a87deef691860f4b549a9a3ba8fc1f68 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 7 Jan 2025 14:17:22 -0500
Subject: [PATCH 3/3] tweak

---
 packages/svelte/src/motion/tweened.js | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/packages/svelte/src/motion/tweened.js b/packages/svelte/src/motion/tweened.js
index 62958a05e76e..36d32d1f72e5 100644
--- a/packages/svelte/src/motion/tweened.js
+++ b/packages/svelte/src/motion/tweened.js
@@ -230,9 +230,6 @@ export class Tween {
 	set(value, options) {
 		set(this.#target, value);
 
-		let previous_task = this.#task;
-
-		let started = false;
 		let {
 			delay = 0,
 			duration = 400,
@@ -241,10 +238,7 @@ export class Tween {
 		} = { ...this.#defaults, ...options };
 
 		if (duration === 0) {
-			if (previous_task) {
-				previous_task.abort();
-				previous_task = null;
-			}
+			this.#task?.abort();
 			set(this.#current, value);
 			return Promise.resolve();
 		}
@@ -253,6 +247,8 @@ export class Tween {
 
 		/** @type {(t: number) => T} */
 		let fn;
+		let started = false;
+		let previous_task = this.#task;
 
 		this.#task = loop((now) => {
 			if (now < start) {