Adding item in redux store array seems to just update it

Question

I am trying to create a cash register system. Now I want to create an order list, which contains products and how many of each I sold. I am using redux store here.

My problem is when I use the ADDORDERITEM case, it receives an action.order like {id: 1, name:"halve zolen", categoryId:1, price: 1.0} for example. In the case statement, the numberOfOrderItems gets set to what number is at that moment in the state.numberOfOrderItems. This works for one item, but if I add the same item with a different amount, I end up with an array with 2 objects with the amount that was last entered, while this should be 2 different amounts here. If I check action.order after I set the numberOfOrderItems it is a correct order, so what is going wrong here? My guess it has something to do with me using state.numberOfOrderItems here which make a subscription to that, and updates it whenever this variable is used somewhere. Is there some way to just take a snapshot of it and never update it again?

My code: Store.js:

import {createStore} from 'redux';

const kassaReducer = (state = {orders: [], numberOfOrderItems: ""}, action) => {
    switch (action.type){
        case "ADDORDERITEM":            
            let newOrder = action.order;          
            newOrder.numberOfOrderItems = state.numberOfOrderItems;
            return {orders: [...state.orders, newOrder], numberOfOrderItems: ""};
        case "REMOVEORDERITEM":
            return {orders : state.orders.remove(state.orders.indexOf(action.order)), numberOfOrderItems: state.numberOfOrderItems};
        case "SETITEMNUMBER":
            return {orders : state.orders, numberOfOrderItems: state.numberOfOrderItems === "" ? action.numberOfOrderItems : (state.numberOfOrderItems + action.numberOfOrderItems)};
    }
    return state;
}

const store = createStore(kassaReducer);

export default store;

Answer 1

Edit: Ok I read your post one more time

This still is invalid and is causing problems:

action.order.numberOfOrderItems = state.numberOfOrderItems;

but it should be:

case "ADDORDERITEM":
  return {orders: [...state.orders, action.order], numberOfOrderItems: state.numberOfOrderItems + action.numberOfOrderItems };