javascript - "TypeError: s.sum is not a function"尝试计算 javascript 对象的总属性值

Question

我有一个 js 对象 JSON

var s = [  
   {  
      "MONTH":"  2018-01",
      "DEPARTMENT":"Legals",
      "EMPLOYEE":"Smith A.",
      "AMOUNT":"14289.66"
   },
   {  
      "MONTH":"  2018-01",
      "DEPARTMENT":"Legals",
      "EMPLOYEE":"Jonson B.",
      "AMOUNT":"7408.05"
   },
   {  
      "MONTH":"  2018-01",
      "DEPARTMENT":"Legals",
      "EMPLOYEE":"Lee C.",
      "AMOUNT":"10102.98"
   }
]

我想计算 AMOUNT 属性的总和，并使用 next 来完成它(我使用了源 stackoverflow_count_summ 中的代码):

s.sum = function(items, prop){
    return items.reduce( function(a, b){
        return a + b[prop];
    }, 0);
};

sTotal = s.sum(s, 'AMOUNT');

但我收到一条错误消息:“TypeError: s.sum 不是函数”

如何通过对象获取“AMOUNT”值的总和？

Answer 1

尝试使用此代码:

var s = [  
   {  
      "MONTH":"  2018-01",
      "DEPARTMENT":"Legals",
      "EMPLOYEE":"Smith A.",
      "AMOUNT":"14289.66"
   },
   {  
      "MONTH":"  2018-01",
      "DEPARTMENT":"Legals",
      "EMPLOYEE":"Jonson B.",
      "AMOUNT":"7408.05"
   },
   {  
      "MONTH":"  2018-01",
      "DEPARTMENT":"Legals",
      "EMPLOYEE":"Lee C.",
      "AMOUNT":"10102.98"
   }
];
s.__proto__.sum = function(items, prop){
    return items.reduce( function(a, b){
        return a + +b[prop];
    }, 0);
};

sTotal = s.sum(s, 'AMOUNT');
console.log(sTotal);

我将函数设置为 proto 并添加类型转换作为返回。我在 Firefox、Chrome 和 Edge 中测试了它，效果很好。