React Redux update item quantity (more than just one increment)

I have a site where the user can increase the quantity on the product before adding it to cart. Now if the user decided to go back to the product and add 3 more by increasing the quantity on the product, then adding to cart – how do I update the quantity of the existing product in basket?

At the moment I get duplicates of the product with different quantities depending on what is selected.

Here is the code I have for my reducer:

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

const initialState = {
  items: [],

const basket = createSlice({
  name: "basket",
  reducers: {
    addToBasket: (state, { payload }) => {
        // No idea what to do with this..
      state.items.filter((pizza) => ===;

      // This pushes the item fine, but I get multiple of the same item in the cart instead of just updating its quantity

      // =>
      // ===
      //       ? {
      // ,
      //           quantity: pizza.quantity + payload.quantity,
      //         }
      //       : pizza
      //   );


export const { addToBasket } = basket.actions;
export const basketItems = (state) => state.basket.items;

export default basket.reducer;

The payload is the specific product, it will be an object:

 name: "product name",
 image: "url.jpeg",
 price: "14.99"

I can not for the life of me figure out what to do here in order not to mutate the state. Nothing works, I feel like I have tried every possible way but clearly I am missing something.

Any help much appreciated!!!


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