对对象数组中的嵌套对象值求和

如何解决对对象数组中的嵌套对象值求和

我有一个对象数组 -

[{
    title: "oranges",id: 5802537,cart: {
      purchased: 3,stockTotal: 9
    },price: 3,department: "fresh fruit and veg"
  },{
    title: "pasta",cart: {
      purchased: 2,stockTotal: 15
    },price: 1,department: "dry goods"
  },{
    title: "eggs",cart: {
      purchased: 1,stockTotal: 11
    },price: 2,department: "baking"
  }
]

我正在尝试编写一个函数，将所有的 stockTotal 相加并从每个对象购买。 我试过这个 -

let val = items.reduce(function(prevIoUsValue,currentValue) {
  return {
    purchased: prevIoUsValue.cart.purchased + currentValue.cart.purchased,stockTotal: prevIoUsValue.cart.stockTotal + currentValue.cart.stockTotal
  };
});

console.log(val);

但是，它说它无法读取未定义的属性“purchased”，也无法读取未定义的属性“stockTotal”。 我想知道这是不是因为 stockTotal 和 purchase 位于数组中每个对象内的它们自己的对象中？

解决方法

const data = [{title:"oranges",id:5802537,cart:{purchased:3,stockTotal:9},price:3,department:"fresh fruit and veg"},{title:"pasta",cart:{purchased:2,stockTotal:15},price:1,department:"dry goods"},{title:"eggs",cart:{purchased:1,stockTotal:11},price:2,department:"baking"}];

let purchased = 0,//set initial values
  stockTotal = 0;
for (let item of data) { // loop items
  purchased += item.cart.purchased; // increment initial values
  stockTotal += item.cart.stockTotal;
}
console.log(purchased,stockTotal);