doc.yeswiki.pro/node_modules/body-scroll-lock/lib/bodyScrollLock.es6.js

// Older browsers don't support event options, feature detect it.

// Adopted and modified solution from Bohdan Didukh (2017)
// https://stackoverflow.com/questions/41594997/ios-10-safari-prevent-scrolling-behind-a-fixed-overlay-and-maintain-scroll-posi

let hasPassiveEvents = false;
if (typeof window !== 'undefined') {
  const passiveTestOptions = {
    get passive() {
      hasPassiveEvents = true;
      return undefined;
    }
  };
  window.addEventListener('testPassive', null, passiveTestOptions);
  window.removeEventListener('testPassive', null, passiveTestOptions);
}

const isIosDevice = typeof window !== 'undefined' && window.navigator && window.navigator.platform && (/iP(ad|hone|od)/.test(window.navigator.platform) || window.navigator.platform === 'MacIntel' && window.navigator.maxTouchPoints > 1);


let locks = [];
let documentListenerAdded = false;
let initialClientY = -1;
let previousBodyOverflowSetting;
let previousBodyPosition;
let previousBodyPaddingRight;

// returns true if `el` should be allowed to receive touchmove events.
const allowTouchMove = el => locks.some(lock => {
  if (lock.options.allowTouchMove && lock.options.allowTouchMove(el)) {
    return true;
  }

  return false;
});

const preventDefault = rawEvent => {
  const e = rawEvent || window.event;

  // For the case whereby consumers adds a touchmove event listener to document.
  // Recall that we do document.addEventListener('touchmove', preventDefault, { passive: false })
  // in disableBodyScroll - so if we provide this opportunity to allowTouchMove, then
  // the touchmove event on document will break.
  if (allowTouchMove(e.target)) {
    return true;
  }

  // Do not prevent if the event has more than one touch (usually meaning this is a multi touch gesture like pinch to zoom).
  if (e.touches.length > 1) return true;

  if (e.preventDefault) e.preventDefault();

  return false;
};

const setOverflowHidden = options => {
  // If previousBodyPaddingRight is already set, don't set it again.
  if (previousBodyPaddingRight === undefined) {
    const reserveScrollBarGap = !!options && options.reserveScrollBarGap === true;
    const scrollBarGap = window.innerWidth - document.documentElement.clientWidth;

    if (reserveScrollBarGap && scrollBarGap > 0) {
      const computedBodyPaddingRight = parseInt(window.getComputedStyle(document.body).getPropertyValue('padding-right'), 10);
      previousBodyPaddingRight = document.body.style.paddingRight;
      document.body.style.paddingRight = `${computedBodyPaddingRight + scrollBarGap}px`;
    }
  }

  // If previousBodyOverflowSetting is already set, don't set it again.
  if (previousBodyOverflowSetting === undefined) {
    previousBodyOverflowSetting = document.body.style.overflow;
    document.body.style.overflow = 'hidden';
  }
};

const restoreOverflowSetting = () => {
  if (previousBodyPaddingRight !== undefined) {
    document.body.style.paddingRight = previousBodyPaddingRight;

    // Restore previousBodyPaddingRight to undefined so setOverflowHidden knows it
    // can be set again.
    previousBodyPaddingRight = undefined;
  }

  if (previousBodyOverflowSetting !== undefined) {
    document.body.style.overflow = previousBodyOverflowSetting;

    // Restore previousBodyOverflowSetting to undefined
    // so setOverflowHidden knows it can be set again.
    previousBodyOverflowSetting = undefined;
  }
};

const setPositionFixed = () => window.requestAnimationFrame(() => {
  // If previousBodyPosition is already set, don't set it again.
  if (previousBodyPosition === undefined) {
    previousBodyPosition = {
      position: document.body.style.position,
      top: document.body.style.top,
      left: document.body.style.left
    };

    // Update the dom inside an animation frame 
    const { scrollY, scrollX, innerHeight } = window;
    document.body.style.position = 'fixed';
    document.body.style.top = -scrollY;
    document.body.style.left = -scrollX;

    setTimeout(() => window.requestAnimationFrame(() => {
      // Attempt to check if the bottom bar appeared due to the position change
      const bottomBarHeight = innerHeight - window.innerHeight;
      if (bottomBarHeight && scrollY >= innerHeight) {
        // Move the content further up so that the bottom bar doesn't hide it
        document.body.style.top = -(scrollY + bottomBarHeight);
      }
    }), 300);
  }
});

const restorePositionSetting = () => {
  if (previousBodyPosition !== undefined) {
    // Convert the position from "px" to Int
    const y = -parseInt(document.body.style.top, 10);
    const x = -parseInt(document.body.style.left, 10);

    // Restore styles
    document.body.style.position = previousBodyPosition.position;
    document.body.style.top = previousBodyPosition.top;
    document.body.style.left = previousBodyPosition.left;

    // Restore scroll
    window.scrollTo(x, y);

    previousBodyPosition = undefined;
  }
};

// https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollHeight#Problems_and_solutions
const isTargetElementTotallyScrolled = targetElement => targetElement ? targetElement.scrollHeight - targetElement.scrollTop <= targetElement.clientHeight : false;

const handleScroll = (event, targetElement) => {
  const clientY = event.targetTouches[0].clientY - initialClientY;

  if (allowTouchMove(event.target)) {
    return false;
  }

  if (targetElement && targetElement.scrollTop === 0 && clientY > 0) {
    // element is at the top of its scroll.
    return preventDefault(event);
  }

  if (isTargetElementTotallyScrolled(targetElement) && clientY < 0) {
    // element is at the bottom of its scroll.
    return preventDefault(event);
  }

  event.stopPropagation();
  return true;
};

export const disableBodyScroll = (targetElement, options) => {
  // targetElement must be provided
  if (!targetElement) {
    // eslint-disable-next-line no-console
    console.error('disableBodyScroll unsuccessful - targetElement must be provided when calling disableBodyScroll on IOS devices.');
    return;
  }

  // disableBodyScroll must not have been called on this targetElement before
  if (locks.some(lock => lock.targetElement === targetElement)) {
    return;
  }

  const lock = {
    targetElement,
    options: options || {}
  };

  locks = [...locks, lock];

  if (isIosDevice) {
    setPositionFixed();
  } else {
    setOverflowHidden(options);
  }

  if (isIosDevice) {
    targetElement.ontouchstart = event => {
      if (event.targetTouches.length === 1) {
        // detect single touch.
        initialClientY = event.targetTouches[0].clientY;
      }
    };
    targetElement.ontouchmove = event => {
      if (event.targetTouches.length === 1) {
        // detect single touch.
        handleScroll(event, targetElement);
      }
    };

    if (!documentListenerAdded) {
      document.addEventListener('touchmove', preventDefault, hasPassiveEvents ? { passive: false } : undefined);
      documentListenerAdded = true;
    }
  }
};

export const clearAllBodyScrollLocks = () => {
  if (isIosDevice) {
    // Clear all locks ontouchstart/ontouchmove handlers, and the references.
    locks.forEach(lock => {
      lock.targetElement.ontouchstart = null;
      lock.targetElement.ontouchmove = null;
    });

    if (documentListenerAdded) {
      document.removeEventListener('touchmove', preventDefault, hasPassiveEvents ? { passive: false } : undefined);
      documentListenerAdded = false;
    }

    // Reset initial clientY.
    initialClientY = -1;
  }

  if (isIosDevice) {
    restorePositionSetting();
  } else {
    restoreOverflowSetting();
  }

  locks = [];
};

export const enableBodyScroll = targetElement => {
  if (!targetElement) {
    // eslint-disable-next-line no-console
    console.error('enableBodyScroll unsuccessful - targetElement must be provided when calling enableBodyScroll on IOS devices.');
    return;
  }

  locks = locks.filter(lock => lock.targetElement !== targetElement);

  if (isIosDevice) {
    targetElement.ontouchstart = null;
    targetElement.ontouchmove = null;

    if (documentListenerAdded && locks.length === 0) {
      document.removeEventListener('touchmove', preventDefault, hasPassiveEvents ? { passive: false } : undefined);
      documentListenerAdded = false;
    }
  }

  if (isIosDevice) {
    restorePositionSetting();
  } else {
    restoreOverflowSetting();
  }
};