Section 4.4.2 -> Function on-change

[pwhittin]

In order to create what I believe to be the intended behavior I needed to make the definition of the "on-change" function the following:

(defn on-change
  [event]
  (let [target (.-target event)
        value-string (.-value target)]
    (if (str/blank? value-string)
      (set! (.-innerHTML result) "----")
      (let [value (read-string value-string)]
        (if (leap? value)
          (set! (.-innerHTML result) "YES")
          (set! (.-innerHTML result) "NO"))))))