cart.selectors.js

import { createSelector } from "reselect";

const selectCart = state => state.cart;

export const selectCartItems = createSelector(
  [selectCart],
  cart => cart.cartItems
);

export const selectCartItemsCount = createSelector(
  [selectCartItems],
  cartItems =>
    cartItems.reduce(
      (accumulatedQuantity, item) => accumulatedQuantity + item.quantity,
      0
    )
);