Question

我有一个对象数组。每个对象都具有一个“ amount”属性，该属性具有一个整数值，例如30000。我想使用reduce对其求和，但是它返回undefined。

如果我console.log（）currentValue.amount返回值，没问题。我不太明白为什么在添加它们时会返回undefined。

let items = [
     { id: 0, name: "Food", amount: 30000 },
     { id: 1, name: "Insurance", amount: 25000 },
     { id: 2, name: "Rent", amount: 50000 }
   ]

    let total = items.reduce((a, b) => {
       console.log(b.amount); // 30000 (first loop)
       a + b.amount; // undefined
     }, 0);
     console.log(total);

当然，我的预期结果是它将对值求和，最后将为变量“总计”分配每个对象的数量属性值的总和。

编辑：我忘了退货！

   let items = [
         { id: 0, name: "Food", amount: 30000 },
         { id: 1, name: "Insurance", amount: 25000 },
         { id: 2, name: "Rent", amount: 50000 }
       ]

   let total = items.reduce((a, b) => {
       console.log(b.amount); // 30000 (first loop)
       return a + b.amount; // 105000 OK
     }, 0);
     console.log(total);

Answer 1

return累加器。

let items = [{
    id: 0,
    name: "Food",
    amount: 30000
  },
  {
    id: 1,
    name: "Insurance",
    amount: 25000
  },
  {
    id: 2,
    name: "Rent",
    amount: 50000
  }
]

let total = items.reduce((a, b) => {
  return a + b.amount;
}, 0);
console.log(total);

Answer 2

使用return，

Reduce函数必须返回一些东西，然后将其用作下一次迭代的函数的第一个参数。

let items = [
     { id: 0, name: "Food", amount: 30000 },
     { id: 1, name: "Insurance", amount: 25000 },
     { id: 2, name: "Rent", amount: 50000 }
   ]

let total = items.reduce((a, b) => {
  return a + b.amount;
}, 0);
console.log(total);

Answer 3

Array.prototype.reduce通过从函数返回累加器来工作。您已经在第二行中忘记了return关键字。

let items = [{id:0,name:"Food",amount:30000},{id:1,name:"Insurance",amount:25000},{id:2,name:"Rent",amount:50000}];

let total = items.reduce((a, b) => {
  console.log(b.amount); 
  return a + b.amount; 
}, 0);

console.log("Total:", total);

您还可以使用解构和箭头函数的隐式返回，如下所示：

let items = [{id:0,name:"Food",amount:30000},{id:1,name:"Insurance",amount:25000},{id:2,name:"Rent",amount:50000}];

let total = items.reduce((a, { amount: b }) => (console.log(b), a + b), 0);

console.log("Total:", total);

尝试使用reduce求和数组对象的属性：未定义？

3 个答案: