code: function getScrollbarWidth() {
  
      if ( $html.height() <= $window.height() ) {
          return 0
      }
  
      var $outer = $( '<div style="visibility:hidden;width:100px" />' ).
          appendTo( 'body' )
  
      // Get the width without scrollbars.
      var widthWithoutScroll = $outer[0].offsetWidth
  
      // Force adding scrollbars.
      $outer.css( 'overflow', 'scroll' )
  
      // Add the inner div.
      var $inner = $( '<div style="width:100%" />' ).appendTo( $outer )
  
      // Get the width with scrollbars.
      var widthWithScroll = $inner[0].offsetWidth
  
      // Remove the divs.
      $outer.remove()
  
      // Return the difference between the widths.
      return widthWithoutScroll - widthWithScroll
  }
docs: Get the width of the browser’s scrollbar.
  Taken from: https://github.com/VodkaBears/Remodal/blob/master/src/jquery.remodal.js