Get the scrollbar width

scrollbar.cljs

;; Adapted from http://stackoverflow.com/a/8079681
(defonce scrollbar-width
  (let [inner (.createElement js/document "p")
        outer (.createElement js/document "div")]
    (doto (.-style inner)
      (aset "width" "100%")
      (aset "height" "500px"))
    (doto (.-style outer)
      (aset "position" "absolute")
      (aset "top" "0px")
      (aset "left" "0px")
      (aset "visibility" "hidden")
      (aset "background" "red")
      (aset "width" "200px")
      (aset "height" "150px")
      (aset "overflow" "hidden"))
    (.appendChild outer inner)
    (.appendChild (.-body js/document) outer)
    (let [w1 (.-offsetWidth inner)
          _  (aset (.-style outer) "overflow" "scroll")
          w2 (.-offsetWidth inner)
          w2 (if (= w1 w2) (.-clientWidth outer) w2)]
      (.removeChild (.-body js/document) outer)
      (- w1 w2))))