doc: create initialState and reducer method

src/redux/reducer.js

@@ -0,0 +1,18 @@
+export const initialState = {
+  basket: [],
+};
+
+const reducer = (state, action) => {
+  switch (action.type) {
+    case "ADD_TO_BASKET":
+      return {
+        ...state,
+        basket: [...state.basket, action.item],
+      };
+
+    default:
+      return state;
+  }
+};
+
+export default reducer;