Merge pull request #682 from hypothesis/allow-multiple-handlers-for-action

Allow multiple state modules to handle the same action

src/sidebar/reducers/index.js

@@ -37,14 +37,14 @@ function init(settings) {
   );
 }
 
-var update = util.createReducer(Object.assign(
+var update = util.createReducer(...[
   annotations.update,
   frames.update,
   links.update,
   selection.update,
   session.update,
-  viewer.update
-));
+  viewer.update,
+]);
 
 module.exports = {
   init: init,

src/sidebar/reducers/test/util-test.js

@@ -68,6 +68,26 @@ describe('reducer utils', function () {
         annotations: [{id: 1}],
       });
     });
+
+    it('applies update functions from each input object', () => {
+      var firstCounterActions = {
+        INCREMENT_COUNTER(state) {
+          return { firstCounter: state.firstCounter + 1 };
+        },
+      };
+      var secondCounterActions = {
+        INCREMENT_COUNTER(state) {
+          return { secondCounter: state.secondCounter + 1 };
+        },
+      };
+      var reducer = util.createReducer(firstCounterActions, secondCounterActions);
+
+      var state =  { firstCounter: 5, secondCounter: 10 };
+      var action = { type: 'INCREMENT_COUNTER' };
+      var newState = reducer(state, action);
+
+      assert.deepEqual(newState, { firstCounter: 6, secondCounter: 11 });
+    });
   });
 
   describe('#bindSelectors', function () {

src/sidebar/reducers/util.js

@@ -11,16 +11,28 @@ function actionTypes(updateFns) {
 }
 
 /**
- * Given an object which maps action names to update functions, this returns
- * a reducer function that can be passed to the redux `createStore` function.
+ * Given objects which map action names to update functions, this returns a
+ * reducer function that can be passed to the redux `createStore` function.
+ *
+ * @param {Object[]} actionToUpdateFn - Objects mapping action names to update
+ *                                      functions.
  */
-function createReducer(updateFns) {
-  return function (state, action) {
-    var fn = updateFns[action.type];
-    if (!fn) {
+function createReducer(...actionToUpdateFn) {
+  // Combine the (action name => update function) maps together into a single
+  // (action name => update functions) map.
+  var actionToUpdateFns = {};
+  actionToUpdateFn.forEach(map => {
+    Object.keys(map).forEach(k => {
+      actionToUpdateFns[k] = (actionToUpdateFns[k] || []).concat(map[k]);
+    });
+  });
+
+  return (state, action) => {
+    var fns = actionToUpdateFns[action.type];
+    if (!fns) {
       return state;
     }
-    return Object.assign({}, state, fn(state, action));
+    return Object.assign({}, state, ...fns.map(f => f(state, action)));
   };
 }