for和forEach循环不适用于对象数组

Question

我有一组自定义对象，我想用Shortcut循环进行迭代，但这在每次返回“ 0”时均不起作用。
for(var i =0;i<array.length;i++)就像一个符咒

这是我的课

var Product = (function () {
    var nextId = 0;
    return function Product(name, quantity, price, picture) {
        this.id = nextId++;
        this.name = name;
        this.quantityInStock = quantity;
        this.price = price;
        this.picture = picture;
    }
})();

var Cart = (function () {
    var nextId = 0;
    return function Cart(productList) {
        this.id = nextId++;
        this.productList = (productList === undefined || !productList instanceof Array) ? [] : productList;
    }
})();
Cart.prototype.addProduct = function (product) {
    (product instanceof Product) ? this.productList.push(product) : console.log("Invalid object type");
};
Cart.prototype.calculateLumpSum = function () {
    var sum = 0;
    this.productList.forEach(function (product) { // doesn't work as well as for in loop
        sum += product.price;
    });
    return sum;
};

请帮助我的错在哪里，再简单的循环效果很好

编辑

for in和forEach循环都不适用于此数组，例如在调试器中，它表明

for(var product in productList) {

}

在这种情况下，乘积等于"0"但数组正确且已添加项目。

Answer 1

我假设这段代码：

Cart.prototype.calculateLumpSum = function () {
    var sum = 0;
    for(var product in this.productList) {
        sum += product.price;
    }
    return sum;
};

如果product.price存在并且具有价值，那么这将完美地工作。