update-val.clj

(require '[cljs-bean.core :refer [->clj ->js]])

(defn update-vals
  "m f => {k (f v) ...}
  Given a map m and a function f of 1-argument, returns a new map where the keys of m
  are mapped to result of applying f to the corresponding values of m."
  {:added "1.11"}
  [m f]
  (with-meta
    (persistent!
      (reduce-kv (fn [acc k v] (assoc! acc k (f v)))
                 (if (implements? IEditableCollection m)
                   (transient m)
                   (transient {}))
                 m))
    (meta m)))

(clj->js (update-vals (js->clj #js {:a 1 :b 2 :c 3 :d 4}) inc))
;; => #js {:a 2, :b 3, :c 4, :d 5}

(->js (update-vals (->clj #js {:a 1 :b 2 :c 3 :d 4}) inc))
;; => #js {:a 2, :b 3, :c 4, :d 5}    3.2x faster