Calculate scrollbar width

calc-scrollbar-width.js

/*
.scrollbar-measure {
  width: 100px;
  height: 100px;
  overflow: scroll;
  position: absolute;
  top: -9999px;
}
*/
// Create the measurement node
var scrollDiv = document.createElement("div");
scrollDiv.className = "scrollbar-measure";
document.body.appendChild(scrollDiv);

// Get the scrollbar width
var scrollbarWidth = scrollDiv.offsetWidth - scrollDiv.clientWidth;
console.warn(scrollbarWidth); // Mac:  15

// Delete the DIV 
document.body.removeChild(scrollDiv);