all-settled.cljs

(defn all-settled [promises]
  (js/Promise.
    (fn [resFn _]
      (let [state (atom {:resolutions (vec (repeat (count promises) nil))
                         :counter 0})
            process (fn [idx type]
                      (fn [val]
                        (swap! state
                          (fn [{:keys [resolutions counter]}]
                            {:resolutions (assoc resolutions idx
                                            {:status type
                                             (case type
                                               "fulfilled" :value
                                               "rejected" :reason) val})
                             :counter (inc counter)}))
                        (let [{:keys [counter resolutions]} @state]
                          (when (= (count promises) counter)
                            (resFn resolutions)))))]
        (doall
          (for [[idx promise] (map-indexed list promises)]
            (-> promise
                (.then (process idx "fulfilled"))
                (.catch (process idx "rejected")))))))))