react-native-reanimated/lib/module/reanimated2/animation/repeat.js

More powerful alternative to Animated library for React Native.

import { defineAnimation, getReduceMotionForAnimation } from './util';

// TODO TYPESCRIPT This is a temporary type to get rid of .d.ts file.

export const withRepeat = function (_nextAnimation) {
  'worklet';

  let numberOfReps = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 2;
  let reverse = arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : false;
  let callback = arguments.length > 3 ? arguments[3] : undefined;
  let reduceMotion = arguments.length > 4 ? arguments[4] : undefined;
  return defineAnimation(_nextAnimation, () => {
    'worklet';

    const nextAnimation = typeof _nextAnimation === 'function' ? _nextAnimation() : _nextAnimation;
    function repeat(animation, now) {
      const finished = nextAnimation.onFrame(nextAnimation, now);
      animation.current = nextAnimation.current;
      if (finished) {
        animation.reps += 1;
        // call inner animation's callback on every repetition
        // as the second argument the animation's current value is passed
        if (nextAnimation.callback) {
          nextAnimation.callback(true /* finished */, animation.current);
        }
        if (animation.reduceMotion || numberOfReps > 0 && animation.reps >= numberOfReps) {
          return true;
        }
        const startValue = reverse ? nextAnimation.current : animation.startValue;
        if (reverse) {
          nextAnimation.toValue = animation.startValue;
          animation.startValue = startValue;
        }
        nextAnimation.onStart(nextAnimation, startValue, now, nextAnimation.previousAnimation);
        return false;
      }
      return false;
    }
    const repCallback = finished => {
      if (callback) {
        callback(finished);
      }
      // when cancelled call inner animation's callback
      if (!finished && nextAnimation.callback) {
        nextAnimation.callback(false /* finished */);
      }
    };

    function onStart(animation, value, now, previousAnimation) {
      animation.startValue = value;
      animation.reps = 0;

      // child animations inherit the setting, unless they already have it defined
      // they will have it defined only if the user used the `reduceMotion` prop
      if (nextAnimation.reduceMotion === undefined) {
        nextAnimation.reduceMotion = animation.reduceMotion;
      }

      // don't start the animation if reduced motion is enabled and
      // the animation would end at its starting point
      if (animation.reduceMotion && reverse && (numberOfReps <= 0 || numberOfReps % 2 === 0)) {
        animation.current = animation.startValue;
        animation.onFrame = () => true;
      } else {
        nextAnimation.onStart(nextAnimation, value, now, previousAnimation);
      }
    }
    return {
      isHigherOrder: true,
      onFrame: repeat,
      onStart,
      reps: 0,
      current: nextAnimation.current,
      callback: repCallback,
      startValue: 0,
      reduceMotion: getReduceMotionForAnimation(reduceMotion)
    };
  });
};
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