Get scroll bar width

getScrollBarWidth.js

// function from 
// https://evilmartians.com/chronicles/scroll-to-the-future-modern-javascript-css-scrolling-implementations
function getScrollBarWidth() {
  const outer = document.createElement('div');
  const inner = document.createElement('div');
  
  outer.style.overflow = 'scroll';
  outer.appendChild(inner);

  document.body.appendChild(outer);
  const scrollBarWidth = outer.offsetWidth - inner.offsetWidth;
  document.body.removeChild(outer);

  return scrollBarWidth;
}