initial_payload.cljs

(re-frame/reg-fx
  ::send-several-ws
  (fn [[websocket payloads]]
    (doseq [p payloads]
      (.send websocket (js/JSON.stringify (clj->js p))))))

(re-frame/reg-event-fx
  ::subscribe
  (fn [{:keys [db]} [_ subscription-id query variables callback-event initial-payload :as event]]
    ;; ...
    (cond
      ;; ...
      (get-in db [:re-graph :websocket :ready?])
      {:db (assoc-in db [:re-graph :subscriptions (name subscription-id)] {:callback callback-event
                                                                           :event event
                                                                           :active? true})
       ::send-several-ws [(get-in db [:re-graph :websocket :connection])
                          [{:id (name subscription-id)
                            :type "connection_init"
                            :payload initial-payload}
                           {:id (name subscription-id)
                            :type "start"
                            :payload {:query (str "subscription " (string/replace query #"^subscription\s?" ""))
                                      :variables variables}}]]})))

      ;; ...)))