作业：
product对象增加字段buy:1，默认购买1
增加输入框和库存显示：
库存：{{ product.inventory }}
<input :disabled="!product.inventory" type="number" v-model="product.buy" style="width:30px;">
修改addProductToCart
addProductToCart ({ state, commit }, product) {
    console.log('addProductToCart',product.buy)
    commit(CART.SET_CHECKOUT_STATUS, null)
   //增加超库存判断
    if (product.buy>product.inventory){
      alert('库存不足'+product.buy)
      return
    }
    if (product.inventory > 0) {
      const cartItem = state.items.find(item => item.id === product.id)
      if (!cartItem) {
        commit(CART.PUSH_PRODUCT_TO_CART, { id: product.id, buy: product.buy })//增加buy参数
      } else {
        commit(CART.INCREMENT_ITEM_QUANTITY, cartItem) //cartItem中已有buy字段
      }
      // remove 1 item from stock
     //扣减库存增加buy字段
      commit(`products/${PRODUCTS.DECREMENT_PRODUCT_INVENTORY}`, { id: product.id, buy: product.buy }, { root: true })
    }
  }
}
//具体3个方法对product.buy进行增加或扣减
1. 扣减库存buy
[PRODUCTS.DECREMENT_PRODUCT_INVENTORY] (state, { id,buy }) {
    const product = state.all.find(product => product.id === id)
    //product.inventory--
    product.inventory -= buy
  }
2. 首次购买增加buy
  [CART.PUSH_PRODUCT_TO_CART] (state, { id,buy }) {
    state.items.push({
      id,
      //quantity: 1
      quantity:buy
    })
  },
//重复购买增加buy
[CART.INCREMENT_ITEM_QUANTITY] (state, { id,buy }) {
    const cartItem = state.items.find(item => item.id === id)
    //cartItem.quantity++
    cartItem.quantity+=buy
  },

现在回复不知道还有没用，但是代码好像有错，ShoppingCart.vue文件中。
   <ul>
      <li
        v-for="product in products"
        :key="product.id">
        {{ product.title }} - {{ product.price }} x {{ product.quantity }}
      </li>
    </ul>
这里的key好想错了，你的代码逻辑里面product没有id。
cartProducts: (state, getters, rootState) => {
    return state.items.map(({ id, quantity }) => {
      const product = rootState.products.all.find(product => product.id === id)
      return {
        title: product.title,
        price: product.price,
        quantity
      }
    })
  },

[CART.SET_CART_ITEMS] (state, { items }) {
    state.items = items
  },

  [CART.SET_CHECKOUT_STATUS] (state, status) {
    state.checkoutStatus = status
  }
}
    commit(CART.SET_CHECKOUT_STATUS, null)
    // empty cart
    commit(CART.SET_CART_ITEMS, { items: [] })
    shop.buyProducts(
      products,
      () => commit(CART.SET_CHECKOUT_STATUS, 'successful'),
      () => {
        commit(CART.SET_CHECKOUT_STATUS, 'failed')
        // rollback to the cart saved before sending the request
        commit(CART.SET_CART_ITEMS, { items: savedCartItems })
      }
    )

老师您好，我想问下 [CART.SET_CHECKOUT_STATUS] 这样写是什么操作呢？
commit(CART.SET_CHECKOUT_STATUS, null)还有就是这样写？看不太懂

辅助函数mapState和mapGetters有哪些区别？是否可以将ProductList.vue文件中
computed: mapState({
   products: state => state.products.all,
})
的写法改为在 product.js 文件更改getters如：
const getters = {
   products: state => state.all
}
从而在ProductList.vue中使用
computed: mapGetters('products', ['products'])

commit(`products/${PRODUCTS.DECREMENT_PRODUCT_INVENTORY}`, { id: product.id }, { root: true })

[PRODUCTS.DECREMENT_PRODUCT_INVENTORY] (state, { id }) {
    const product = state.all.find(product => product.id === id)
    product.inventory--
  }

老师不知道 { root: true } 这是什么意思，有什么用？没有看见使用的地方