Google Map component, with reagent and reframe. Questions asked on Clojurians #re-frame's channel.

1_google_map.cljs

; Following code is WRONG, see comments for details.
(defn google-map []
  (let [pos   (subscribe [:current-position])]

    (reagent/create-class
      {:reagent-render 
       (fn []
         [:div
          [:h4 "Map"]
          [:div#map-canvas {:style {:height "400px"}}]])

       :component-did-mount
       (fn []
         (let [map-canvas  (.getElementById js/document "map-canvas")
               map-options (clj->js {"zoom" 9})
               gmap        (js/google.maps.Map. map-canvas map-options)
               marker      (js/google.maps.Marker. (clj->js {:map gmap :title "Drone"}))]

           (reagent.ratom/run!
             (let [latlng (js/google.maps.LatLng. (:latitude @pos) (:longitude @pos))]
               (.setPosition marker latlng)
               (.panTo gmap latlng)))))})))

2_google_map.cljs

; Another attempt, using props and lifecycle to udpate marker position
(defn gmap-component []
  (let [gmap    (atom nil)
        options (clj->js {"zoom" 9})
        update  (fn [comp]
                  (let [{:keys [latitude longitude]} (reagent/props comp)
                        latlng (js/google.maps.LatLng. latitude longitude)]
                    (.setPosition (:marker @gmap) latlng)
                    (.panTo (:map @gmap) latlng)))]

    (reagent/create-class
      {:reagent-render (fn []
                         [:div
                          [:h4 "Map"]
                          [:div#map-canvas {:style {:height "400px"}}]])

       :component-did-mount (fn [comp]
                              (let [canvas  (.getElementById js/document "map-canvas")
                                    gm      (js/google.maps.Map. canvas options)
                                    marker  (js/google.maps.Marker. (clj->js {:map gm :title "Drone"}))]
                                (reset! gmap {:map gm :marker marker}))
                              (update comp))

       :component-did-update update
       :display-name "gmap-component"})))

(defn gmap-wrapper []
  (let [pos (subscribe [:current-position])]
    (fn []
      [gmap-component @pos])))

I feel like if's correct enough it would be a nice addition to https://github.com/reagent-project/reagent-cookbook/tree/master/recipes/google-maps given the re-frame part is replaced with a ratom.

4 was just a consequence of putting the run! at the wrong place, initial comment updated accordingly.
I don't think it was wrong per se but it's now unnecessary once run! is called where it should be.

⚠️ Got some feedback from Re-Frame's author, using run! is very wrong here (if following re-frame approach).

Discussion here: https://clojurians-log.clojureverse.org/reagent/2015-08-05.html

I rewrote it, see https://gist.github.com/jhchabran/e09883c3bc1b703a224d#file-2_google_map-cljs if you're interested :)

It should use will-receive-props for update as we don't interact with the dom as opposed to http://nils-blum-oeste.net/clojurescripts-reagent-using-props-in-lifecycle-hooks/ example.

When using this I have found it important to run :component-will-unmount to dispose of the stateful component