`spring` returns `NaN` and breaks physics simulation when `config` has `undefined` properties

Author: codeCraft-RitikCreated Sep 16, 2026Updated Sep 17, 2026

Labelsbug

Describe the bug

When calling spring() with a config object containing undefined properties (common when passing optional React props: { damping: props.damping, stiffness: props.stiffness }), springCalculation merges the configuration with object spread:

In packages/core/src/spring/spring-utils.ts:

typescript

config: {
  ...defaultSpringConfig,
  ...config,
}

If stiffness or mass is undefined, it overrides defaultSpringConfig's value with undefined. In advance(), Math.sqrt(k / m) calculates Math.sqrt(undefined / 1) = NaN, causing spring() to return NaN for every frame.

If damping is undefined, zeta evaluates to NaN. Because NaN < 1 is false, it bypasses underDampedPosition and silently forces the spring into criticallyDampedPosition, breaking underdamped spring physics without error.

Steps To Reproduce

Call spring with an optional property explicitly set to undefined:

typescript

import { spring } from 'remotion';

const value = spring({
  frame: 10,
  fps: 30,
  config: {
    damping: 10,
    stiffness: undefined,
  },
});

### Expected behavior

### Expected behavior
`springCalculation` should fall back to `defaultSpringConfig` values using nullish coalescing (`config.stiffness ?? defaultSpringConfig.stiffness`), gracefully handling partial and optional configuration objects.

### Suggested Fix
```diff
--- a/packages/core/src/spring/spring-utils.ts
+++ b/packages/core/src/spring/spring-utils.ts
@@ -14,7 +14,7 @@ export type SpringConfig = {
 	overshootClamping: boolean;
 };
 
-const defaultSpringConfig: SpringConfig = {
+export const defaultSpringConfig: SpringConfig = {
 	damping: 10,
 	mass: 1,
 	stiffness: 100,
@@ -118,12 +118,18 @@ export function springCalculation({
 	const from = 0;
 	const to = 1;
+	const resolvedConfig: SpringConfig = {
+		damping: config.damping ?? defaultSpringConfig.damping,
+		mass: config.mass ?? defaultSpringConfig.mass,
+		stiffness: config.stiffness ?? defaultSpringConfig.stiffness,
+		overshootClamping:
+			config.overshootClamping ?? defaultSpringConfig.overshootClamping,
+	};
 	const cacheKey = [
 		frame,
 		fps,
-		config.damping,
-		config.mass,
-		config.overshootClamping,
-		config.stiffness,
+		resolvedConfig.damping,
+		resolvedConfig.mass,
+		resolvedConfig.overshootClamping,
+		resolvedConfig.stiffness,
 	].join('-');
 	if (calculationCache[cacheKey]) {
 		return calculationCache[cacheKey];
@@ -144,10 +150,7 @@ export function springCalculation({
 		animation = advance({
 			animation,
 			now: time,
-			config: {
-				...defaultSpringConfig,
-				...config,
-			},
+			config: resolvedConfig,
 		});
 	}
 
@@ -156,10 +159,7 @@ export function springCalculation({
 		animation = advance({
 			animation,
 			now: (frameClamped / fps) * 1000,
-			config: {
-				...defaultSpringConfig,
-				...config,
-			},
+			config: resolvedConfig,
 		});
 	}

Packages

@remotion/core

Additional Context

No response

Source: refinedev/refine

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