docusaurus/packages/docusaurus-theme-classic/src/theme/hooks/useScrollPosition.ts

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

import {useEffect, useRef} from 'react';
import ExecutionEnvironment from '@docusaurus/ExecutionEnvironment';
import type {ScrollPosition} from '@theme/hooks/useScrollPosition';

const getScrollPosition = (): ScrollPosition => ({
  scrollX: ExecutionEnvironment.canUseDOM ? window.pageXOffset : 0,
  scrollY: ExecutionEnvironment.canUseDOM ? window.pageYOffset : 0,
});

const useScrollPosition = (
  effect?: (position: ScrollPosition, lastPosition: ScrollPosition) => void,
  deps = [],
): void => {
  const scrollPosition = useRef(getScrollPosition());

  const handleScroll = () => {
    const currentScrollPosition = getScrollPosition();

    if (effect) {
      effect(currentScrollPosition, scrollPosition.current);
    }

    scrollPosition.current = currentScrollPosition;
  };

  useEffect(() => {
    const opts: AddEventListenerOptions & EventListenerOptions = {
      passive: true,
    };

    handleScroll();
    window.addEventListener('scroll', handleScroll, opts);

    return () => window.removeEventListener('scroll', handleScroll, opts);
  }, deps);
};

export default useScrollPosition;