faster-js->clj.cljs

(def kw-cache #js{})

(defn cached-kw [fqn]
  (if-some [kw (unchecked-get kw-cache fqn)]
    kw
    (let [kw (keyword fqn)]
      (unchecked-set kw-cache fqn kw)
      kw)))

(defn js->clj-fast
  [x]
  (let [f (fn thisfn [x]
            (case (js* "typeof ~{}" x)
              "string" x
              "number" x
              "boolean" x

              "object"
              (cond
                (array? x)
                (if (<= (alength x) 32)
                  (.fromArray PersistentVector
                              (amap x idx ret (aset ret idx (thisfn (aget x idx))))
                              true)
                  (mapv thisfn x))

                (identical? (.-constructor x) js/Object)
                (let [out (array)]
                  (js* "for (var key in ~{}) {~{}.push(~{}(key)); ~{}.push(~{}(~{}[key]));}"
                       x out cached-kw out thisfn x)
                  (if (<= (alength out) 16)
                    (.fromArray PersistentArrayMap out true true)
                    (.fromArray PersistentHashMap out true)))
                
                :else x)
              x))]
    (f x)))

Not for node (due to keyword cache). Almost not tested.