Because not everyone hides the scrollbar on OSX ;) Tiny AMD module that will return you the browsers scrollbar width can be installed via bower, AMD is optional.
Installation
npm install scroll-width --save
yarn add scroll-width
bower install scroll-width --save
require(['scrollWidth'], function(scrollWidth){
alert("My scroll's width is " + scrollWidth + "px");
});
alert("My scroll's width is " + window.scrollWidth + "px");