add a getInitialState method to store

Author: EskiMojo14

src/createStore.ts

@@ -138,6 +138,7 @@ export function createStore<
   let currentState: S | PreloadedState | undefined = preloadedState as
     | PreloadedState
     | undefined
+  let initialState: S | PreloadedState | undefined = currentState
   let currentListeners: Map<number, ListenerCallback> | null = new Map()
   let nextListeners = currentListeners
   let listenerIdCounter = 0
@@ -176,6 +177,15 @@ export function createStore<
     return currentState as S
   }
 
+  /**
+   * Reads the initial state tree managed by the store.
+   *
+   * @returns The initial state tree of your application.
+   */
+  function getInitialState(): S {
+    return initialState as S
+  }
+
   /**
    * Adds a change listener. It will be called any time an action is dispatched,
    * and some part of the state tree may potentially have changed. You may then
@@ -385,10 +395,14 @@ export function createStore<
   // the initial state tree.
   dispatch({ type: ActionTypes.INIT } as A)
 
+  // initial state should be the state *after* the "INIT" action is dispatched
+  initialState = currentState
+
   const store = {
     dispatch: dispatch as Dispatch<A>,
     subscribe,
     getState,
+    getInitialState,
     replaceReducer,
     [$$observable]: observable
   } as unknown as Store<S, A, StateExt> & Ext

src/types/store.ts

@@ -118,6 +118,8 @@ export interface Store<
    */
   getState(): S & StateExt
 
+  getInitialState(): S & StateExt
+
   /**
    * Adds a change listener. It will be called any time an action is
    * dispatched, and some part of the state tree may potentially have changed.

test/createStore.spec.ts

@@ -24,10 +24,11 @@ describe('createStore', () => {
     // So we filter it out
     const methods = Object.keys(store).filter(key => key !== $$observable)
 
-    expect(methods.length).toBe(4)
+    expect(methods.length).toBe(5)
     expect(methods).toContain('subscribe')
     expect(methods).toContain('dispatch')
     expect(methods).toContain('getState')
+    expect(methods).toContain('getInitialState')
     expect(methods).toContain('replaceReducer')
   })
 
@@ -926,4 +927,55 @@ describe('createStore', () => {
       )
     ).toThrow()
   })
+
+  it("exposes getInitialState which returns the store's initial state", () => {
+    const unPreloadedStore = createStore(reducers.todos)
+
+    expect(unPreloadedStore.getInitialState()).toEqual([])
+
+    unPreloadedStore.dispatch(addTodo('Hello'))
+
+    expect(unPreloadedStore.getInitialState()).toEqual([])
+
+    expect(unPreloadedStore.getState()).toEqual([
+      {
+        id: 1,
+        text: 'Hello'
+      }
+    ])
+
+    const preloadedStore = createStore(reducers.todos, [
+      {
+        id: 1,
+        text: 'Hello'
+      }
+    ])
+
+    expect(preloadedStore.getInitialState()).toEqual([
+      {
+        id: 1,
+        text: 'Hello'
+      }
+    ])
+
+    preloadedStore.dispatch(addTodo('World'))
+
+    expect(preloadedStore.getInitialState()).toEqual([
+      {
+        id: 1,
+        text: 'Hello'
+      }
+    ])
+
+    expect(preloadedStore.getState()).toEqual([
+      {
+        id: 1,
+        text: 'Hello'
+      },
+      {
+        id: 2,
+        text: 'World'
+      }
+    ])
+  })
 })