Add composeReducers (#33)

Add composeReducers

README.md

@@ -352,3 +352,34 @@ Example
 ```ts
 setPrefix("MY_APP");
 ```
+
+### `function composeReducers<State>(...reducers)`
+
+Utility that reduces actions by applying them through multiple reducers.
+This helps in allowing you to split up your reducer logic to multiple `ImmerReducer`s
+if they affect the same part of your state
+
+Example
+
+```ts
+class MyNameReducer extends ImmerReducer<NamesState> {
+    setFirstName(firstName: string) {
+        this.draftState.firstName = firstName;
+    }
+
+    setLastName(lastName: string) {
+        this.draftState.lastName = lastName;
+    }
+}
+
+class MyAgeReducer extends ImmerReducer<AgeState> {
+    setAge(age: number) {
+        this.draftState.age = 8;
+    }
+}
+
+export const reducer = composeReducers(
+  createReducerFunction(MyNameReducer, initialState),
+  createReducerFunction(MyAgeReducer, initialState)
+)
+```

__tests__/immer-reducer.test.tsx

@@ -2,6 +2,7 @@ import {
     ImmerReducer,
     createReducerFunction,
     createActionCreators,
+    composeReducers,
     setPrefix,
     _clearKnownClasses,
     isAction,
@@ -10,35 +11,11 @@ import {
 
 import {createStore, combineReducers, Action} from "redux";
 
-interface Reducer<State> {
-    (state: State | undefined, action: any): State;
-}
-
 beforeEach(_clearKnownClasses);
 
 afterEach(() => {
     setPrefix("IMMER_REDUCER");
 });
-/**
- * Combine multiple reducers into a single one
- *
- * @param reducers two or more reducer
- */
-function composeReducers<State>(
-    ...reducers: (Reducer<State | undefined>)[]
-): Reducer<State> {
-    return (state: any, action: any) => {
-        return (
-            reducers.reduce((state, subReducer) => {
-                if (typeof subReducer === "function") {
-                    return subReducer(state, action);
-                }
-
-                return state;
-            }, state) || state
-        );
-    };
-}
 
 test("can create reducers", () => {
     const initialState = {foo: "bar"};

src/immer-reducer.ts

@@ -142,6 +142,31 @@ export function isActionFrom<T extends ImmerReducerClass>(
     return isActionFromClass(action, immerReducerClass);
 }
 
+interface Reducer<State> {
+    (state: State | undefined, action: any): State;
+}
+
+/**
+ * Combine multiple reducers into a single one
+ *
+ * @param reducers two or more reducer
+ */
+export function composeReducers<State>(
+    ...reducers: (Reducer<State | undefined>)[]
+): Reducer<State> {
+    return (state: any, action: any) => {
+        return (
+            reducers.reduce((state, subReducer) => {
+                if (typeof subReducer === "function") {
+                    return subReducer(state, action);
+                }
+
+                return state;
+            }, state) || state
+        );
+    };
+}
+
 /** The actual ImmerReducer class */
 export class ImmerReducer<T> {
     static customName?: string;