src/utilities/getScrollBarWidth.js

/**
 * Get scroll bar's width.
 * @example
 * const scrollBarWidth = bse.utilities.getScrollBarWidth();
 * @return {number} Page's scroll bar width even if there is no scroll bar.
 * Return 0 if scroll bar is transparent(Eg: Safari on iPhone/iPad).
 */
export default function getScrollBarWidth() {
  const inner = document.createElement('p');
  inner.style.width = '100%';
  inner.style.height = '200px';

  const outer = document.createElement('div');
  outer.style.position = 'absolute';
  outer.style.top = '0px';
  outer.style.left = '0px';
  outer.style.visibility = 'hidden';
  outer.style.width = '200px';
  outer.style.height = '150px';
  outer.style.overflow = 'hidden';
  outer.appendChild(inner);

  document.body.appendChild(outer);
  const w1 = inner.offsetWidth;
  outer.style.overflow = 'scroll';
  let w2 = inner.offsetWidth;
  if (w1 === w2) w2 = outer.clientWidth;

  document.body.removeChild(outer);

  return w1 - w2;
}