problem with using strings as cursors in Om

om-string-cursor.cljs

; Suggested in Om Basic Tutorial for making strings work as cursors
(extend-type string
  ICloneable
  (-clone [s] (js/String. s)))
(extend-type js/String
  ICloneable
  (-clone [s] (js/String. s))
  om/IValue
  (-value [s] (str s)))

(def app-state (atom {:text "Foo"}))

(om/root
  (fn [app owner]
    (dom/h1 nil
      (let [text (:text app)]
        (if (= "Foo" text) "Passed." "Failed."))))
  app-state
  {:target (. js/document (getElementById "app"))})