Polyfill experimental 'spring()' timing function for native

Uses React Native Animated API to polyfill a 2016 proposal for the
spring() timing function in CSS.

https://lists.w3.org/Archives/Public/www-style/2016Jun/0181.html

Author: necolas

apps/examples/src/components/App.js

@@ -739,7 +739,7 @@ const styles = css.create({
     backgroundColor: 'red',
     transitionDuration: '500ms',
     transitionProperty: 'transform',
-    transitionTimingFunction: 'ease'
+    transitionTimingFunction: 'spring(1,100,10,0)'
   },
   objContain: {
     objectFit: 'contain'

packages/react-strict-dom/src/native/modules/useStyleTransition.js

@@ -8,6 +8,7 @@
  */
 
 import type {
+  CompositeAnimation,
   ReactNativeStyle,
   ReactNativeStyleValue,
   ReactNativeTransform
@@ -191,6 +192,38 @@ function transitionStyleHasChanged(
   return false;
 }
 
+function getAnimation(
+  animatedValue: Animated.Value,
+  duration: number,
+  timingFunction: string | null,
+  shouldUseNativeDriver: boolean
+): CompositeAnimation {
+  // Based on https://lists.w3.org/Archives/Public/www-style/2016Jun/0181.html
+  // spring(mass, stiffness, damping, initialVelocity)
+  if (timingFunction != null && timingFunction.includes('spring')) {
+    const chunk = timingFunction.split('spring(')[1];
+    const str = chunk.split(')')[0];
+    const [mass = 1, stiffness = 100, damping = 10, initialVelocity = 0] =
+      str === '' ? [] : str.split(',').map((point) => parseFloat(point.trim()));
+
+    return Animated.spring(animatedValue, {
+      damping,
+      mass,
+      stiffness,
+      toValue: 1,
+      useNativeDriver: shouldUseNativeDriver,
+      velocity: initialVelocity
+    });
+  }
+
+  return Animated.timing(animatedValue, {
+    duration,
+    easing: getEasingFunction(timingFunction),
+    toValue: 1,
+    useNativeDriver: shouldUseNativeDriver
+  });
+}
+
 export function useStyleTransition(style: ReactNativeStyle): ReactNativeStyle {
   const {
     transitionDelay: _delay,
@@ -260,12 +293,12 @@ export function useStyleTransition(style: ReactNativeStyle): ReactNativeStyle {
 
       const animation = Animated.sequence([
         Animated.delay(delay),
-        Animated.timing(animatedValue, {
-          toValue: 1,
+        getAnimation(
+          animatedValue,
           duration,
-          easing: getEasingFunction(timingFunction),
-          useNativeDriver: shouldUseNativeDriver
-        })
+          timingFunction,
+          shouldUseNativeDriver
+        )
       ]);
       animation.start();
 

packages/react-strict-dom/src/types/renderer.native.js

@@ -9,6 +9,10 @@
 
 // $FlowFixMe(nonstrict-import)
 import type AnimatedNode from 'react-native/Libraries/Animated/nodes/AnimatedNode';
+import type {
+  // $FlowFixMe(nonstrict-import)
+  CompositeAnimation
+} from 'react-native/Libraries/Animated/Animated';
 import type {
   // $FlowFixMe(nonstrict-import)
   Props as TextInputProps
@@ -141,6 +145,7 @@ type ReactNativeStyleValue =
 type ReactNativeStyle = { [string]: ?ReactNativeStyleValue };
 
 export type {
+  CompositeAnimation,
   ReactNativeProps,
   ReactNativeStyle,
   ReactNativeStyleValue,

packages/react-strict-dom/tests/__mocks__/react-native/index.js

@@ -30,6 +30,11 @@ export const Animated = {
       }),
       stop: jest.fn()
     };
+  }),
+  spring: jest.fn(() => {
+    return {
+      start: jest.fn()
+    };
   })
 };
 

packages/react-strict-dom/tests/__snapshots__/html-test.native.js.snap-native

@@ -1043,7 +1043,7 @@ exports[`<html.*> style polyfills "transition" properties  backgroundColor trans
 />
 `;
 
-exports[`<html.*> style polyfills "transition" properties  cubic-bezier easing: end 1`] = `
+exports[`<html.*> style polyfills "transition" properties  cubic-bezier() timing function: end 1`] = `
 <Animated.View
   animated={true}
   style={
@@ -1065,7 +1065,7 @@ exports[`<html.*> style polyfills "transition" properties  cubic-bezier easing:
 />
 `;
 
-exports[`<html.*> style polyfills "transition" properties  cubic-bezier easing: start 1`] = `
+exports[`<html.*> style polyfills "transition" properties  cubic-bezier() timing function: start 1`] = `
 <Animated.View
   animated={true}
   style={
@@ -1328,6 +1328,41 @@ exports[`<html.*> style polyfills "transition" properties  other transforms: tra
 />
 `;
 
+exports[`<html.*> style polyfills "transition" properties  spring() timing function: end 1`] = `
+<Animated.View
+  animated={true}
+  style={
+    {
+      "boxSizing": "content-box",
+      "opacity": {
+        "inputRange": [
+          0,
+          1,
+        ],
+        "outputRange": [
+          1,
+          0,
+        ],
+      },
+      "position": "static",
+    }
+  }
+/>
+`;
+
+exports[`<html.*> style polyfills "transition" properties  spring() timing function: start 1`] = `
+<Animated.View
+  animated={true}
+  style={
+    {
+      "boxSizing": "content-box",
+      "opacity": 1,
+      "position": "static",
+    }
+  }
+/>
+`;
+
 exports[`<html.*> style polyfills "transition" properties  transform transition: end 1`] = `
 <Animated.View
   animated={true}

packages/react-strict-dom/tests/html-test.native.js

@@ -701,10 +701,9 @@ describe('<html.*>', () => {
         expect(Easing.out).toHaveBeenCalled();
       });
 
-      test('cubic-bezier easing', () => {
+      test('cubic-bezier() timing function', () => {
         const BEZIER_STR = 'cubic-bezier( 0.1,  0.2,0.3  ,0.4)';
         let root;
-        // cubic-bezier easing
         act(() => {
           root = create(<html.div style={styles.opacity(1, BEZIER_STR)} />);
         });
@@ -717,6 +716,35 @@ describe('<html.*>', () => {
         expect(Easing.bezier).toHaveBeenCalledWith(0.1, 0.2, 0.3, 0.4);
       });
 
+      test('spring() timing function', () => {
+        // spring(mass, stiffness, damping, initialVelocity)
+        const SPRING_STR = 'spring( 1,  2,3  , 4 )';
+        let root;
+        act(() => {
+          root = create(<html.div style={styles.opacity(1, SPRING_STR)} />);
+        });
+        expect(root.toJSON()).toMatchSnapshot('start');
+        expect(Animated.spring).not.toHaveBeenCalled();
+        expect(Animated.timing).not.toHaveBeenCalled();
+        act(() => {
+          root.update(<html.div style={styles.opacity(0, SPRING_STR)} />);
+        });
+        expect(root.toJSON()).toMatchSnapshot('end');
+        // Animated.spring(damping, mass, stiffness, toValue, useNativeDriver, velocity)
+        expect(Animated.spring).toHaveBeenCalledWith(
+          expect.anything(),
+          expect.objectContaining({
+            damping: 3,
+            mass: 1,
+            stiffness: 2,
+            toValue: 1,
+            useNativeDriver: true,
+            velocity: 4
+          })
+        );
+        expect(Animated.timing).not.toHaveBeenCalled();
+      });
+
       test('transition all properties (opacity and transform)', () => {
         let root;
         // transition all properties (opacity and transform)