(defn tree-seq [branch? children root]
 (eduction (take-while some?) (map #(aget % 0))
  (iterate (fn [[node pair]]
          (when-some [[[node' & r] cont] (if (branch? node)
                                               (if-some [cs (not-empty (children node))]
                                                 #js [cs pair]
                                                 pair)
                                               pair)]
            (if (some? r)
              #js [node' #js [r cont]]
              #js [node' cont])))
     #js [root nil])))