Throw new error when initial state is undefined

packages/toolkit/src/createSlice.ts

@@ -262,6 +262,16 @@ export function createSlice<
   if (!name) {
     throw new Error('`name` is a required option for createSlice')
   }
+
+  if (
+    typeof process !== 'undefined' &&
+    process.env.NODE_ENV === 'development'
+  ) {
+    if(options.initialState === undefined) {
+      console.error('You must provide an `initialState` value that is not `undefined`. You may have misspelled `initialState`')
+    }
+  }
+
   const initialState =
     typeof options.initialState == 'function'
       ? options.initialState

packages/toolkit/src/tests/createSlice.test.ts

@@ -1,7 +1,18 @@
 import type { PayloadAction } from '@reduxjs/toolkit'
 import { createSlice, createAction } from '@reduxjs/toolkit'
+import {
+  mockConsole,
+  createConsole,
+  getLog,
+} from 'console-testing-library/pure'
 
 describe('createSlice', () => {
+  let restore: () => void
+
+  beforeEach(() => {
+    restore = mockConsole(createConsole())
+  })
+
   describe('when slice is undefined', () => {
     it('should throw an error', () => {
       expect(() =>
@@ -34,6 +45,18 @@ describe('createSlice', () => {
     })
   })
 
+  describe('when initial state is undefined', () => {
+    it('should throw an error', () => {
+      createSlice({
+        name: 'test',
+        reducers: {},
+        initialState: undefined,
+      })
+
+      expect(getLog().log).toBe('You must provide an `initialState` value that is not `undefined`. You may have misspelled `initialState`')
+    })
+  })
+
   describe('when passing slice', () => {
     const { actions, reducer, caseReducers } = createSlice({
       reducers: {