code-lab/node_modules/vuetify/lib/composables/scroll.mjs

// Utilities
import { computed, onBeforeUnmount, onMounted, ref, shallowRef, watch } from 'vue';
import { clamp, consoleWarn, propsFactory } from "../util/index.mjs"; // Types
// Composables
export const makeScrollProps = propsFactory({
  scrollTarget: {
    type: String
  },
  scrollThreshold: {
    type: [String, Number],
    default: 300
  }
}, 'scroll');
export function useScroll(props) {
  let args = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : {};
  const {
    canScroll
  } = args;
  let previousScroll = 0;
  let previousScrollHeight = 0;
  const target = ref(null);
  const currentScroll = shallowRef(0);
  const savedScroll = shallowRef(0);
  const currentThreshold = shallowRef(0);
  const isScrollActive = shallowRef(false);
  const isScrollingUp = shallowRef(false);
  const scrollThreshold = computed(() => {
    return Number(props.scrollThreshold);
  });

  /**
   * 1: at top
   * 0: at threshold
   */
  const scrollRatio = computed(() => {
    return clamp((scrollThreshold.value - currentScroll.value) / scrollThreshold.value || 0);
  });
  const onScroll = () => {
    const targetEl = target.value;
    if (!targetEl || canScroll && !canScroll.value) return;
    previousScroll = currentScroll.value;
    currentScroll.value = 'window' in targetEl ? targetEl.pageYOffset : targetEl.scrollTop;
    const currentScrollHeight = targetEl instanceof Window ? document.documentElement.scrollHeight : targetEl.scrollHeight;
    if (previousScrollHeight !== currentScrollHeight) {
      previousScrollHeight = currentScrollHeight;
      return;
    }
    isScrollingUp.value = currentScroll.value < previousScroll;
    currentThreshold.value = Math.abs(currentScroll.value - scrollThreshold.value);
  };
  watch(isScrollingUp, () => {
    savedScroll.value = savedScroll.value || currentScroll.value;
  });
  watch(isScrollActive, () => {
    savedScroll.value = 0;
  });
  onMounted(() => {
    watch(() => props.scrollTarget, scrollTarget => {
      const newTarget = scrollTarget ? document.querySelector(scrollTarget) : window;
      if (!newTarget) {
        consoleWarn(`Unable to locate element with identifier ${scrollTarget}`);
        return;
      }
      if (newTarget === target.value) return;
      target.value?.removeEventListener('scroll', onScroll);
      target.value = newTarget;
      target.value.addEventListener('scroll', onScroll, {
        passive: true
      });
    }, {
      immediate: true
    });
  });
  onBeforeUnmount(() => {
    target.value?.removeEventListener('scroll', onScroll);
  });

  // Do we need this? If yes - seems that
  // there's no need to expose onScroll
  canScroll && watch(canScroll, onScroll, {
    immediate: true
  });
  return {
    scrollThreshold,
    currentScroll,
    currentThreshold,
    isScrollActive,
    scrollRatio,
    // required only for testing
    // probably can be removed
    // later (2 chars chlng)
    isScrollingUp,
    savedScroll
  };
}
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