javascript - 下面代码的输出是 NaN，为什么？

Question

在这里，我尝试添加“order_total”属性。我已经使用了reduce方法，如果只尝试数组，相同的代码可以正常工作，但是当我在对象数组上实现时，它会产生NaN。

var user = {
    id: 16,
    username: 'smith',
    email: '<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="60130d09140820070d01090c4e030f0d" rel="noreferrer noopener nofollow">[email protected]</a>',
    order: [
        {
            id: 71,
            order_number: 'DCT-123',
            order_total: 12000,
        },
        {
            id: 71,
            order_number: 'DCT-345',
            order_total: 7000,
        },
        {
            id: 71,
            order_number: 'DCT-321',
            order_total: 2000,
        }
    ]
};

var result = user.order.reduce(function(a, b) {
    return a.order_total + b.order_total;
}); 

console.log(result); 

Answer 1

reduce回调中的参数a是累加器，而不是对象的属性。请参阅here了解有关减少的更多信息

var user = {
    id: 16,
    username: 'smith',
    email: '<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="3e4d53574a567e59535f5752105d5153" rel="noreferrer noopener nofollow">[email protected]</a>',
    order: [
        {
            id: 71,
            order_number: 'DCT-123',
            order_total: 12000,
        },
        {
            id: 71,
            order_number: 'DCT-345',
            order_total: 7000,
        },
        {
            id: 71,
            order_number: 'DCT-321',
            order_total: 2000,
        }
    ]
};

var result = user.order.reduce(function(a, b) {
    return a+b.order_total;
},0); 

console.log(result);