Question

我有一个对象数组，我想在我的对象中为整个数组求和所有“bps”值。

我的对象数组如下所示：

arr = [
    {
        date: "2017-06-14T14:00:00.000Z",
        bps: 2
    },
    ...
]

这是我的缩减功能：

arr.reduce((accum, currVal) => {
        console.log(accum.bps);
        console.log(currVal.bps);
        console.log(accum.bps + currVal.bps);
        return accum.bps + currVal.bps;
    }, {
        bps: 0
    });

根据输出到控制台的内容，似乎在reduce函数的第一次迭代之后，返回值0不会成为下一个迭代的累加器（它变为“未定义”）。为什么会出现这种情况，我的函数应该如何总结我的数组中的所有“bps”值？

控制台正在显示

scripts.js:1024 0
scripts.js:1025 0
scripts.js:1026 0
scripts.js:1024 undefined
scripts.js:1025 0
scripts.js:1026 NaN
scripts.js:1024 undefined
scripts.js:1025 0
scripts.js:1026 NaN
scripts.js:1024 undefined
scripts.js:1025 0
scripts.js:1026 NaN
scripts.js:1024 undefined
scripts.js:1025 0
scripts.js:1026 NaN
scripts.js:1024 undefined
scripts.js:1025 0
scripts.js:1026 NaN
scripts.js:1024 undefined
scripts.js:1025 0
scripts.js:1026 NaN
scripts.js:1024 undefined
scripts.js:1025 0
scripts.js:1026 NaN
scripts.js:1024 undefined
scripts.js:1025 0
scripts.js:1026 NaN
scripts.js:1024 undefined
scripts.js:1025 0
scripts.js:1026 NaN
scripts.js:1024 undefined
scripts.js:1025 0
scripts.js:1026 NaN
scripts.js:1024 undefined
scripts.js:1025 1.95
scripts.js:1026 NaN
scripts.js:1024 undefined
scripts.js:1025 0
scripts.js:1026 NaN
scripts.js:1024 undefined
scripts.js:1025 0
scripts.js:1026 NaN
scripts.js:1031 NaN

Answer 1

由于您的reduce只是将所有.bps值一起添加，您可以简单地将所有数组项映射到数字数组，然后将它们一起添加

arr.map(({bps}) => bps)
.reduce((a, b) => a + b);

甚至

arr.reduce((accum, {bps}) => accum + bps, 0);

Answer 2

您应该返回一个具有<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.0.0/jquery.min.js"></script> <input value="1000"/>键的对象，而不是纯粹的总和。

即。 bps代替return { bps: accum.bps + currVal.bps };

return accum.bps + currVal.bps;

<击> 或者（这实际上会更快，特别是对于长数组，因为它不会创建不必要的对象，只会创建结果对象。）

arr .reduce((accum, currVal) => { console.log(accum.bps); console.log(currVal.bps); console.log(accum.bps + currVal.bps); return { bps: accum.bps + currVal.bps }; }, { bps: 0 }) .bps;

<击>

Answer 3

这很有效。 accum是一个数字，所以不要使用accum.bps。此外，初始值是一个数字，所以不要使用{bps：0}，只需使用0。

arr = [{
    date: "2017-06-14T14:00:00.000Z",
    bps: 2
}, {
    date: "2017-05-14T14:00:00.000Z",
    bps: 9
}, {
    date: "2017-08-14T14:00:00.000Z",
    bps: 4
}]

// Here is my reduce function:

arr.reduce((accum, currVal) => {
    console.log("accum-" + accum);
    console.log("currVal.bps-" + currVal.bps);
    console.log("return value-" + (accum + currVal.bps));
    return accum + currVal.bps;
}, 0);

这是输出：

accum-0
currVal.bps-2
return value-2
accum-2
currVal.bps-9
return value-11
accum-11
currVal.bps-4
return value-15

为什么我的reduce函数中的累加器不会采用回调的返回值？

3 个答案: