Keeping state between Figwheel reloads

example.cljs

;;;;;;;; actually, (defonce state (new-state)) solves all of this.
;;;;;;;; thanks @bhauman for pointing this out!
;;;;;;;; https://twitter.com/bhauman/status/508328343201005568
;;;;;;;; ---------------------------------------------------------

;; How to keep state atom between Figwheel reloads?

(ns example
  (:require [cljs.reader :refer [read-string]]))

(defn new-state []
  {:counter 0})

(def local-storage-key "example-state")

(defn save-to-local-storage! [new-state]
  ;; for use in add-watch inner function
  (let [serialized (pr-str new-state)]
    (.setItem js/localStorage local-storage-key serialized)))

(defn load-from-local-storage! []
  (when-let [state (.getItem js/localStorage local-storage-key)]
    (read-string state)))

(let [loaded-state (load-from-local-storage!)]
  (defonce state (atom
                   (if (nil? loaded-state)
                     (new-state)
                     loaded-state))))

(add-watch state :state
           (fn [_ _ _ new-state]
             (save-to-local-storage! new-state)))

(fw/watch-and-reload
  ;; ... maybe :jsload-callback for React's render-component etc.
  )

;; With this, Figwheel will keep your state atom between reloads!