Question

如何通过比较两个数组中的书籍 ID 来添加书籍作者

2021-07-06

168

javascript arrays performance loops object

var books = [
  {id: 1, title: "Javascript"},
  {id: 2, title: "PHP"},
  {id: 3, title: "Dart"},
  {id: 4, title: "C++"}
]
var authors = [
  {book_id: 1, user: {id: 1, name: "John Doe"}},
  {book_id: 3, user: {id: 4, name: "Alex Rio"}},
  {book_id: 4, user: {id: 42, name: "Paul Radmond"}}
]

for(var i = 0; i < books.length; i++) {
  let bookAuthor = authors.find(author => {
    return author.book_id === books[i].id
  })

  console.log(bookAuthor.user)
  
  // Push user key from authors to current book item by book id
}

循环结果：

{
  id:1,
  name:"John Doe"
}

error: Uncaught TypeError: Cannot read property 'user' of undefined

在此循环中第一次找到用户，但第二次返回错误。

我如何才能正确（高效地）根据我的情况将图书用户按 ID 推送到 books 数组项？

结果必须是这样的：

var books = [
    {id: 1, title: "Javascript", user: {id: 1, name: "John Doe"}},
    {id: 2, title: "PHP"},
    {id: 3, title: "Dart", user: {id: 4, name: "Alex Rio"}},
    {id: 4, title: "C++", user: {id: 42, name: "Paul Radmond"}}
]

Answer 1

你离得太近了。只需检查是否找到了作者。如果找到，则将用户对象添加到书籍对象。按照此操作-

const books = [
  {id: 1, title: "Javascript"},
  {id: 2, title: "PHP"},
  {id: 3, title: "Dart"},
  {id: 4, title: "C++"}
];
const authors = [
  {book_id: 1, user: {id: 1, name: "John Doe"}},
  {book_id: 3, user: {id: 4, name: "Alex Rio"}},
  {book_id: 4, user: {id: 42, name: "Paul Radmond"}}
];

const result = books.map(book => {
  const author = authors.find(author => author.book_id === book.id);
  
  if (author) {
    book.user = author.user;
  }
  
  return book
});

console.log(result);

.as-console-wrapper { min-height: 100% !important; top: 0}

Answer 2

你可以按照这种方式进行

const result = books.map(book => {
  const author = authors.find(author => author.book_id === book.id)
  if(author) return {...book, user: author}
  return book;
})