Add DeepPartial type for preloaded state (#2679)

Author: aikoven

index.d.ts

@@ -194,6 +194,8 @@ export interface Store<S = any, A extends Action = Action, N = never> {
   replaceReducer(nextReducer: Reducer<S, A>): void;
 }
 
+export type DeepPartial<T> = { [K in keyof T]?: DeepPartial<T[K]> };
+
 /**
  * A store creator is a function that creates a Redux store. Like with
  * dispatching function, we must distinguish the base store creator,
@@ -206,7 +208,7 @@ export interface Store<S = any, A extends Action = Action, N = never> {
  */
 export interface StoreCreator {
   <S, A extends Action, N>(reducer: Reducer<S, A>, enhancer?: StoreEnhancer<N>): Store<S, A, N>;
-  <S, A extends Action, N>(reducer: Reducer<S, A>, preloadedState: S, enhancer?: StoreEnhancer<N>): Store<S, A, N>;
+  <S, A extends Action, N>(reducer: Reducer<S, A>, preloadedState: DeepPartial<S>, enhancer?: StoreEnhancer<N>): Store<S, A, N>;
 }
 
 /**
@@ -230,7 +232,7 @@ export interface StoreCreator {
  */
 export type StoreEnhancer<N = never> = (next: StoreEnhancerStoreCreator<N>) => StoreEnhancerStoreCreator<N>;
 export type GenericStoreEnhancer<N = never> = StoreEnhancer<N>;
-export type StoreEnhancerStoreCreator<N = never> = <S = any, A extends Action = Action>(reducer: Reducer<S, A>, preloadedState?: S) => Store<S, A, N>;
+export type StoreEnhancerStoreCreator<N = never> = <S = any, A extends Action = Action>(reducer: Reducer<S, A>, preloadedState?: DeepPartial<S>) => Store<S, A, N>;
 
 /**
  * Creates a Redux store that holds the state tree.

test/typescript/store.ts

@@ -5,20 +5,29 @@ import {
 
 
 type State = {
-  todos: string[];
+  a: 'a';
+  b: {
+    c: 'c',
+    d: 'd',
+  };
 }
 
-const reducer: Reducer<State> = (state: State, action: Action): State => {
+const reducer: Reducer<State> = (state: State | undefined = {
+  a: 'a',
+  b: {
+    c: 'c',
+    d: 'd',
+  },
+}, action: Action): State => {
   return state;
-}
-
+};
 
 /* createStore */
 
 const store: Store<State> = createStore(reducer);
 
 const storeWithPreloadedState: Store<State> = createStore(reducer, {
-  todos: []
+  b: {c: 'c'}
 });
 
 const genericEnhancer: GenericStoreEnhancer = <S>(next: StoreEnhancerStoreCreator<S>) => next;
@@ -28,7 +37,7 @@ const storeWithGenericEnhancer: Store<State> = createStore(reducer, genericEnhan
 const storeWithSpecificEnhancer: Store<State> = createStore(reducer, specificEnhancer);
 
 const storeWithPreloadedStateAndEnhancer: Store<State> = createStore(reducer, {
-  todos: []
+  b: {c: 'c'}
 }, genericEnhancer);