循环对象，并在数组中累计返回每个键的长度。

Question

我有一个对象，我想遍历它，并返回数组中每个键的累积长度。下面是对象和理想输出：

const books = {
    "book_1": ["image-1", "image-2", "image-3"], // 3
    "book_2": ["image-1"], // 1
    "book_3": ["image-1", "image-2"] // 2
}

// Ideal Output
[3, 4, 6]

我知道不可能在一个对象上循环，但是我使用了Object.key()和.reduce()来获取每个键的长度，我只是想不出如何将它们拼凑在一起。任何帮助都将不胜感激。

​

const books = {
    "book_1": ["image-1", "image-2", "image-3"], // 3
    "book_2": ["image-1"], // 1
    "book_3": ["image-1", "image-2"] // 2
}

console.log(Object.keys(books).reduce(function (accumulator, currentValue, index) {
  console.log(books[Object.keys(books)[index]].length)
  
  return currentValue;
}, []))

​

Answer 1

​

const books = {
    "book_1": ["image-1", "image-2", "image-3"], // 3
    "book_2": ["image-1"], // 1
    "book_3": ["image-1", "image-2"] // 2
}

console.log(Object.entries(books).reduce((acc, [key, array]) => {
  acc.push((acc.slice(-1)[0] || 0) + array.length);
  return acc;
}, []))

​

但是..。由于键订单没有得到保证，所以您可能会以

​

const books = {
    "book_2": ["image-1"], // 1
    "book_1": ["image-1", "image-2", "image-3"], // 3
    "book_3": ["image-1", "image-2"] // 2
}

console.log(Object.entries(books).reduce((acc, [key, array]) => {
  acc.push((acc.slice(-1)[0] || 0) + array.length);
  return acc;
}, []))

​

你想要一个特别的顺序我猜-所以，把钥匙分类

​

const books = {
    "book_2": ["image-1"], // 1
    "book_1": ["image-1", "image-2", "image-3"], // 3
    "book_3": ["image-1", "image-2"] // 2
}

console.log(Object.entries(books).sort(([a], [b]) => a.localeCompare(b)).reduce((acc, [key, array]) => {
  acc.push((acc.slice(-1)[0] || 0) + array.length);
  return acc;
}, []))

​

Answer 2

不过，可以在对象上循环。

const books = {
"book_1": ["image-1", "image-2", "image-3"], // 3
"book_2": ["image-1"], // 1
"book_3": ["image-1", "image-2"] // 2
}

let sum = 0;
let arr = [];

for(let i in books){
  sum += books[i].length;
  arr.push(sum);
}

console.log(arr);//[3,4,6]