createSlice — Slice Basics

import { createSlice } from "@reduxjs/toolkit";


interface CartState {
  items: CartItem[];      // [{ productId, qty }]
}

const initialState: CartState = {
  items: [],
};

const cartSlice = createSlice({
  name: "cart",
  initialState,
  reducers: {
    addItem: (state, action: PayloadAction<CartItem>) => {
      // Immer: mutate করলেও আসল state বদলায় না
      const existing = state.items.find(
        (i) => i.productId === action.payload.productId,
      );
      if (existing) {
        existing.qty += action.payload.qty;
      } else {
        state.items.push(action.payload);
      }
    },
  },
});

export const { addItem } = cartSlice.actions;
export default cartSlice.reducer;

dispatch(addItem({ productId: "p1", qty: 1 }));
// action:  { type: "cart/addItem", payload: { productId: "p1", qty: 1 } }