From 685cb322609defc75c5a8c990551912d58371a6b Mon Sep 17 00:00:00 2001
From: Kern Zhao <siyangkernzhao@gmail.com>
Date: Tue, 24 Sep 2019 10:08:07 -0400
Subject: [PATCH] compose reducer on the fly instead of storing reducer array

---
 modules/store/src/reducer_creator.ts | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/modules/store/src/reducer_creator.ts b/modules/store/src/reducer_creator.ts
index 4f75040a82..e740ac3f94 100644
--- a/modules/store/src/reducer_creator.ts
+++ b/modules/store/src/reducer_creator.ts
@@ -1,4 +1,5 @@
 import { ActionCreator, ActionReducer, ActionType, Action } from './models';
+import { compose } from './utils';
 
 // Return type of the `on` fn.
 export interface On<S> {
@@ -229,14 +230,16 @@ export function createReducer<S, A extends Action = Action>(
   initialState: S,
   ...ons: On<S>[]
 ): ActionReducer<S, A> {
-  const map = new Map<string, ActionReducer<S, A>[]>();
+  const map = new Map<string, ActionReducer<S, A>>();
   for (let on of ons) {
     for (let type of on.types) {
       if (map.has(type)) {
-        const existingReducers = map.get(type) as ActionReducer<S, A>[];
-        map.set(type, [...existingReducers, on.reducer]);
+        const existingReducer = map.get(type) as ActionReducer<S, A>;
+        const newReducer: ActionReducer<S, A> = (state, action) =>
+          on.reducer(existingReducer(state, action), action);
+        map.set(type, newReducer);
       } else {
-        map.set(type, [on.reducer]);
+        map.set(type, on.reducer);
       }
     }
   }