Core Data: Refactor, add comments and avoiding returning new instance…

…s in each selector call

core-data/index.js

@@ -22,7 +22,7 @@ const store = registerStore( MODULE_KEY, {
 			fulfill() {
 				wp.apiRequest( { path: '/wp/v2/categories' } ).then( categories => {
 					store.dispatch( {
-						type: 'FETCH_CATEGORIES_SUCCESS',
+						type: 'RECEIVE_CATEGORIES',
 						categories,
 					} );
 				} );

core-data/reducer.js

@@ -1,13 +1,30 @@
-const reducer = ( state, action ) => {
+/**
+ * External dependencies
+ */
+import { uniqBy } from 'lodash';
+import { combineReducers } from 'redux';
+
+/**
+ * Reducer returning the categories list.
+ *
+ * @param {Object}  state                 Current state.
+ * @param {Object}  action                Dispatched action.
+ *
+ * @return {string} Updated state.
+ */
+function categories( state = [], action ) {
 	switch ( action.type ) {
-		case 'FETCH_CATEGORIES_SUCCESS':
-			return action.categories.reduce( ( memo, category ) => ( {
-				...memo,
-				[ category.id ]: category,
-			} ), {} );
+		case 'RECEIVE_CATEGORIES':
+			return uniqBy(
+				[
+					...action.categories,
+					...state,
+				],
+				( category ) => category.id
+			);
 	}
 
 	return state;
-};
+}
 
-export default reducer;
+export default combineReducers( { categories } );

core-data/selectors.js

@@ -1,5 +1,11 @@
-import { values } from 'lodash';
 
+/**
+ * Returns all the available categories.
+ *
+ * @param {Object} state Global application state.
+ *
+ * @return {Array} Categories List
+ */
 export function getCategories( state ) {
-	return values( state );
+	return state.categories;
 }