feat: allow non-numeric values to be tweened by snapping immediately to new value

Author: Rich-Harris

.changeset/cool-apples-report.md

@@ -0,0 +1,5 @@
+---
+'svelte': minor
+---
+
+feat: allow non-numeric values to be tweened by snapping immediately to new value

packages/svelte/src/motion/tweened.js

@@ -72,7 +72,8 @@ function get_interpolator(a, b) {
 		return (t) => a + t * delta;
 	}
 
-	throw new Error(`Cannot interpolate ${type} values`);
+	// for non-numeric values, snap to the final value immediately
+	return () => b;
 }
 
 /**

packages/svelte/tests/motion/test.ts

@@ -3,6 +3,7 @@ import '../helpers.js'; // for the matchMedia polyfill
 import { describe, it, assert } from 'vitest';
 import { get } from 'svelte/store';
 import { spring, tweened, Tween } from 'svelte/motion';
+import { raf } from '../animation-helpers.js';
 
 describe('motion', () => {
 	describe('spring', () => {
@@ -38,6 +39,16 @@ describe('motion', () => {
 			size.update((v) => v + 10);
 			assert.equal(get(size), 20);
 		});
+
+		it('updates non-numeric values immediately', () => {
+			raf.reset();
+			const boolean = tweened(false);
+
+			boolean.set(true, { duration: 100 });
+
+			raf.tick(1);
+			assert.equal(get(boolean), true);
+		});
 	});
 
 	describe('Tween', () => {
@@ -47,6 +58,16 @@ describe('motion', () => {
 			size.set(100, { duration: 0 });
 			assert.equal(size.current, 100);
 		});
+
+		it('updates non-numeric values immediately', () => {
+			raf.reset();
+			const boolean = new Tween(false);
+
+			boolean.set(true, { duration: 100 });
+
+			raf.tick(1);
+			assert.equal(boolean.current, true);
+		});
 	});
 
 	it('updates correctly when initialized with a `null`-ish value', () => {