now everything works with React ToolKit

client/src/reducers/alert.js

@@ -1,19 +1,20 @@
-import { SET_ALERT, REMOVE_ALERT } from '../actions/types';
+import { createSlice } from "@reduxjs/toolkit";
 
 const initialState = [];
 
-function alertReducer(state = initialState, action) {
-  const { type, payload } = action;
+const alertSlice = createSlice({
+  name: "alert",
+  initialState,
+  reducers: {
+    setAlert(state, action) {
+      return [...state, action.payload];
+    },
+    removeAlert(state, action) {
+      return state.filter((alert) => alert.id !== action.payload);
+    },
+  },
+});
 
-  switch (type) {
-    case SET_ALERT:
-      return [...state, payload];
-    case REMOVE_ALERT:
-      return state.filter((alert) => alert.id !== payload);
-    default:
-      return state;
-  }
-}
+export const { setAlert, removeAlert } = alertSlice.actions;
 
-
-export default alertReducer;
+export default alertSlice.reducer;