如何在JavaScript中使用带有条件的数组化简? [英] How to use array reduce with condition in JavaScript?

问题描述

所以我有一个数组

const records = [
    {
        value: 24,
        gender: "BOYS"
    },
    {
        value: 42,
        gender: "BOYS"
    },
    {
        value: 85,
        gender: "GIRLS"
    },
    {
        value: 12,
        gender: "GIRLS"
    },
    {
        value: 10,
        gender: "BOYS"
    }
]

我想获取 sum ，所以我使用了JavaScript数组reduce函数并正确处理了它.这是我的代码:

And I want to get the sum so I used the JavaScript array reduce function and got it right. Here is my code:

someFunction() {
  return records.reduce(function(sum, record){
    return sum + record.value; 
  }, 0);
}

使用该代码，我得到正确的值 173 .现在，我想做的就是只将所有总和归给具有"BOYS" 性别的那些对象.

With that code I get the value 173 which is correct. Now what I wanted to do is to get all the sum only to those objects who got a "BOYS" gender.

我尝试过类似的事情

someFunction() {
  return records.reduce(function(sum, record){
    if(record.gender == 'BOYS') return sum + record.value; 
  }, 0);
}

但是我什么也没得到.我在这里想念什么吗?任何帮助将不胜感激.

But I get nothing. Am I missing something here? Any help would be much appreciated.

推荐答案

当您从reduce函数中不返回任何内容时，它将返回undefined和undefined + 1 === NaN.相反，您应该在缩小之前对数组进行过滤.

When you return nothing from the reduce function it returns undefined and undefined + 1 === NaN. You should instead filter the array before reducing.

records.filter(({gender}) => gender === 'BOYS')
    .reduce((sum, record) => sum + record.value)

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