from bootstrap modal

getScrollbarWidth.js

function getScrollbarWidth(){
  var scrollDiv = document.createElement('div');
  scrollDiv.style.position = 'absolute';
  scrollDiv.style.top = '-9999px';
  scrollDiv.style.width = '50px';
  scrollDiv.style.height = '50px';
  scrollDiv.style.overflow= 'scroll';
  document.body.appendChild(scrollDiv);
  var scrollbarWidth = scrollDiv.offsetWidth - scrollDiv.clientWidth;
  document.body.removeChild(scrollDiv);
  return scrollbarWidth;
}