Just a gist to explain Redux Toolkit

orderSlice.js

import { createSlice, PayloadAction } from '@reduxjs/toolkit'

export interface OrderState {
  item: string;
  qty: number;
  total: number;
}

const initialState: OrderState = {
  item: "",
  qty: 0,
  total: 0,
}

export const orderSlice = createSlice({
  name: 'order',
  initialState,
  reducers: {
    addItem: (state, action: PayloadAction<string>) => {
      state.item = action.payload
    },
    remItem: (state) => {
      state.item = ""
    },
    incrementQty: (state) => {
      state.qty += 1
    },
    decrementQty: (state) => {
      state.qty -= 1
    },
    incrementTotal: (state, action: PayloadAction<number>) => {
      state.total += action.payload
    },
    decrementTotal: (state, action: PayloadAction<number>) => {
      state.total -= action.payload
    },
  },
})

export const { addItem, remItem, incrementQty, decrementQty, incrementTotal } = orderSlice.actions

export default orderSlice.reducer