javascript - JS - 将键从一个对象移动到另一个对象

Question

我有书籍 list :

let myBooks = [{"id":8,"name":"Don Quijote","author":"Cervantes"},{"id":9,"name":"Romeo and Juliet","author":"Shakespeare"},{"id":10,"name":"Hamlet","author":"Shakespeare"},{"id":11,"name":"Othello","author":"Shakespeare"},{"id":"12","nazev":"Antigona","autor":"Sofokles"}]

我需要找出如何与作者一起创建新对象以及他们在 myBooks 中出现了多少次，如下所示:

let authorsInMyBooks = [{"Cervantes":1},{"Shakespeare":3},{"Sofokles":1}]

我尝试过这个:

for (i = 0; i < myBooks.length; i++) {
            if (myBooks[i].author in authorsInMyBooks) {
                authorsInMyBooks[myBooks[i].author] += 1;
            } else {
                authorsInMyBooks[myBooks[i].author] = 1;
            }
        }

但是输出是:

[{"Cervantes":5, "Shakespeare":9, "Sofokles":1}]

当我将新书添加到 myBooks 时，我每次都会用 for 循环调用函数

Answer 1

或者，您可以使用Array.reduce ( see MDN )，例如:

const myBooks = [
  {"id":8,"name":"Don Quijote","author":"Cervantes"},
  {"id":9,"name":"Romeo and Juliet","author":"Shakespeare"},
  {"id":10,"name":"Hamlet","author":"Shakespeare"},
  {"id":11,"name":"Othello","author":"Shakespeare"},
  {"id":"12","nazev":"Antigona","author":"Sofokles"} ];

const authorFreqs = Object.entries(
  myBooks
    .reduce( (accumulator, value) => 
      ( {...accumulator, [value.author]: accumulator[value.author] 
             ? accumulator[value.author] + 1 
             : 1} ),
      {}) )
    .map( ([key, value]) => ({ [key]: value }) );

console.log(authorFreqs);

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