reduce：长度之和没有产生预期的结果

Question

我正在尝试访问下面列出的这些嵌套数组中的关键“孩子”。我想要一个总数，有多少个孩子。我对编码很陌生，我一直在尝试一些事情，但一直无法解决问题。有帮助吗？

另外，我想使用 reduce 方法来完成这个任务，谢谢！

const characters = [
  {
    name: 'Eddard',
    spouse: 'Catelyn',
    children: ['Robb', 'Sansa', 'Arya', 'Bran', 'Rickon'],
    house: 'Stark',
  },
  {
    name: 'Jon',
    spouse: 'Lysa',
    children: ['Robin'],
    house: 'Arryn',
  },
  {
    name: 'Cersei',
    spouse: 'Robert',
    children: ['Joffrey', 'Myrcella', 'Tommen'],
    house: 'Lannister',
  },
  {
    name: 'Daenarys',
    spouse: 'Khal Drogo',
    children: ['Drogon', 'Rhaegal', 'Viserion'],
    house: 'Targaryen',
  },
  {
    name: 'Mace',
    spouse: 'Alerie',
    children: ['Margaery', 'Loras'],
    house: 'Tyrell',
  },
  {
    name: 'Sansa',
    spouse: 'Tyrion',
    house: 'Stark',
  },
  {
    name: 'Jon',
    spouse: null,
    house: 'Snow',
  },
];

const countNumberOfChildren = (arr) => {
  const selectChildren = arr.reduce((acc, c)=>{
   console.log('this is c', c)
   console.log('this is acc', acc)
   acc + c.children.length()
   console.log('this is acc2', acc)

  return acc
  }, 0)
  console.log(selectChildren) 
};

countNumberOfChildren(characters)

Answer 1

将您的 countNumberOfChildren 函数编辑为

const countNumberOfChildren = (arr) => {
  const selectChildren = arr.reduce((acc, c) =>  acc + (c.children ? c.children.length : 0), 0);
  return selectChildren;    
};

在这里，我们首先检查当前元素 (c) 中是否存在名为“children”的属性。如果存在则将其长度添加到 acc 否则添加 0.

Answer 2

问题在于

acc + c.children.length()

不会更改

acc

变量并且

.length

不是函数，它是属性。此外，所以元素可能没有

.children

属性。

您可以将整个

.reduce()

调用压缩成一行，并使用 optional chaining 和 null coalescing 来处理没有像这样的

.children

数组的元素：

const characters=[{name:'Eddard',spouse:'Catelyn',children:['Robb','Sansa','Arya','Bran','Rickon'],house:'Stark'},{name:'Jon',spouse:'Lysa',children:['Robin'],house:'Arryn'},{name:'Cersei',spouse:'Robert',children:['Joffrey','Myrcella','Tommen'],house:'Lannister'},{name:'Daenarys',spouse:'Khal Drogo',children:['Drogon','Rhaegal','Viserion'],house:'Targaryen'},{name:'Mace',spouse:'Alerie',children:['Margaery','Loras'],house:'Tyrell'},{name:'Sansa',spouse:'Tyrion',house:'Stark'},{name:'Jon',spouse:null,house:'Snow'}];


const numChildren = characters.reduce((acc, curr) => acc + (curr.children?.length ?? 0), 0);
console.log(numChildren);