Get total scroll

easyScroll.js

// returns the total scroll amount in pixels
const getTotalScroll = ({
  isWindow,
  elementToScroll,
  elementWidthProp,
  initialScrollPosition,
  scrollLengthProp
}) => {
  let totalScroll;
  
  if (isWindow) {
    const documentElement = document.documentElement;
    totalScroll = documentElement.offsetWidth
  } else {
    totalScroll = elementToScroll[scrollLengthProp] - elementToScroll[elementLengthProp];
  }
  return totalScroll - initialScrollPosition;
}

function smoothScroll(scrollParams) {
  const elementToScroll = scrollParams.element;
  const isWindow = elementToScroll === window;
  const scrollDirectionProp = isWindow ? 'scrollX' : 'scrollLeft';
  const elementWidthProp = isWindow ? 'innerWidth' : 'clientWidth';
  const scrollLengthProp = 'scrollWidth';
  const initialScrollPosition = elementToScroll[scrollDirectionProp];
  let totalScroll = getTotalScroll({
    isWindow,
    elementToScroll,
    elementWidthProp,
    initialScrollPosition,
    scrollLengthProp
  });
  ...
}