State: hooks 'state-get', 'state-apply'

README.md

@@ -110,3 +110,9 @@ The following values are possible for categories (the only mandatory value is qu
 * const: an object variable which is available as prefix in twig functions.
 
 All values in the "feature" section may use the [TwigJS language](doc/TwigJS.md) for evaluation.
+
+### Hooks
+With the function `register_hook` you can hook into several functions. The following hooks are available:
+
+* `state-get`: modules can add values into the current state. Parameters: `state`: an object, which can be modified by modules.
+* `state-apply`: when a state is applied to the app. Parameters: `state`: state which should be applied.

src/state.js

@@ -20,6 +20,9 @@ function get () {
   state.lon = center.lng
   state.zoom = zoom
 
+  // other modules
+  call_hooks('state-get', state)
+
   // done
   return state
 }
@@ -36,6 +39,9 @@ function apply (state) {
       map.flyTo({ lat: state.lat, lng: state.lon }, state.zoom)
     }
   }
+
+  // other modules
+  call_hooks('state-apply', state)
 }
 
 function stringify (state) {