@devpodio/perfect-scrollbar/src/handlers/click-rail.js

Minimalistic but perfect custom scrollbar plugin

import {updateGeometry} from '../update-geometry';

export default function(i) {
  const element = i.element;

  i.event.bind(i.scrollbarY, 'mousedown', e => e.stopPropagation());
  i.event.bind(i.scrollbarYRail, 'mousedown', e => {
    const positionTop =
      e.pageY -
      window.pageYOffset -
      i.scrollbarYRail.getBoundingClientRect().top;
    const direction = positionTop > i.scrollbarYTop ? 1 : -1;

    i.element.scrollTop += direction * i.containerHeight;
    updateGeometry(i);

    e.stopPropagation();
  });

  i.event.bind(i.scrollbarX, 'mousedown', e => e.stopPropagation());
  i.event.bind(i.scrollbarXRail, 'mousedown', e => {
    const positionLeft =
      e.pageX -
      window.pageXOffset -
      i.scrollbarXRail.getBoundingClientRect().left;
    const direction = positionLeft > i.scrollbarXLeft ? 1 : -1;

    i.element.scrollLeft += direction * i.containerWidth;
    updateGeometry(i);

    e.stopPropagation();
  });
}