editing begin

playground/src/reducers/createReducer.ts

@@ -2,13 +2,23 @@ import { Reducer } from 'redux';
 import { ActionTypes, TodoAction } from '../actions';
 import { Draft, produce } from 'immer';
 
-export function createReducer<T>(
-  initialState: T,
-  handlers: { [actionType in ActionTypes]?: (state: Draft<T>, action: TodoAction) => T }
-): Reducer<T> {
+export type ImmerReducer<T> = (state: Draft<T>, action: TodoAction) => T;
+export type HandlerMap<T> = { [actionType in ActionTypes]?: ImmerReducer<T> };
+
+function isHandlerFunction<T>(handlerOrMap: HandlerMap<T> | ImmerReducer<T>): handlerOrMap is ImmerReducer<T> {
+  if (typeof handlerOrMap === 'function') {
+    return true;
+  }
+
+  return false;
+}
+
+export function createReducer<T>(initialState: T, handlerOrMap: HandlerMap<T> | ImmerReducer<T>): Reducer<T> {
   return function reducer(state = initialState, action: TodoAction): T {
-    if (handlers.hasOwnProperty(action.type)) {
-      return produce(state, draft => handlers[action.type](draft, action));
+    if (isHandlerFunction(handlerOrMap)) {
+      return produce(state, draft => handlerOrMap(draft, action));
+    } else if (handlerOrMap.hasOwnProperty(action.type)) {
+      return produce(state, draft => handlerOrMap[action.type](draft, action));
     } else {
       return state;
     }

playground/src/reducers/index.ts

@@ -1,6 +1,7 @@
 import { createReducer } from './createReducer';
 import { Store, FilterTypes } from '../store';
 import { combineReducers } from 'redux';
+import produce from 'immer';
 
 let counter = 0;
 
@@ -22,12 +23,19 @@ export const reducer = combineReducers<Store>({
       complete(draft, action) {
         draft[action.id].completed = !draft[action.id].completed;
         return draft;
+      },
+
+      clear(draft, action) {
+        Object.keys(draft).forEach(id => {
+          if (draft[id].completed) {
+            delete draft[id];
+          }
+        });
+        return draft;
       }
     }
   ),
-  filter: createReducer<FilterTypes>('all', {
-    filter(draft, action) {
-      return action.filter;
-    }
+  filter: createReducer<Store['filter']>('all', (draft, action) => {
+    return action.filter;
   })
 });