为什么这些 JavaScript 循环不能按预期工作？

Question

我正在尝试为我的 mongoose 数据库创建一个播种器函数，到目前为止我编写的代码实际上有效，我只是无法理解执行操作的顺序。 这是源代码：

var mongoose = require('mongoose'),
    Book = require('./models/book'),
    Chapter = require('./models/chapter');

var books = [
    {
        title: '12 Rules For Life',
        author: 'Jordan B. Peterson',
        cover: '',
        ISBN: 1241232,
        description: 'A self-help book written by Canadian psychologist Jordan B. Peterson',
        status: 'reading'
    },
    {
        title: "Charllote's Web",
        author: 'EB White',
        cover: '',
        ISBN: 1243575,
        description: 'The story of a girl who raises a pig and a spider',
        status: 'read'
    },
    {
        title: 'A Fraction Of The Whole',
        author: 'Steve Toltz',
        cover: '',
        ISBN: 1241686,
        description: 'A book telling the story of three generations of the Toltz family',
        status: 'want to read'
    }
];
var chapters = [
    {
        title: 'First Chapter - How It All Began',
        body: 'This is how it all began'
    }
];

function seedDb() {
    // delete all books and chapters
    Book.deleteMany({}, function(err) {
        if (err) {
            console.log(err);
        } else {
            console.log('Removed all books');
            Chapter.deleteMany({}, function(err) {
                if (err) {
                    console.log(err);
                } else {
                    console.log('Removed all chapters');
                    // add new books to the database from books array
                    books.forEach(function(book) {
                        Book.create(book, function(err, createdBook) {
                            if (err) {
                                console.log(err);
                            } else {
                                console.log('Created The Book ' + createdBook.title);
                                // add new chapters to the book created
                                for (var i = 0; i < chapters.length; i++) {
                                    Chapter.create(chapters[i], function(err, createdComment) {
                                        if (err) {
                                            console.log(err);
                                        } else {
                                            console.log('Created chapter for ' + createdBook.title);
                                            createdBook.chapters.push(createdComment);
                                        }

                                        createdBook.save(function(err) {
                                            if (err) {
                                                console.log(err);
                                            } else {
                                                console.log('Associated Chapter with the book ' + createdBook.title);
                                            }
                                        });
                                    });
                                }
                            }
                        });
                    });
                }
            });
        }
    });
}

module.exports = seedDb;

这是操作发生的顺序：在此处输入图像描述

订单不应该是这样的：

• 删除了所有书籍
• 删除了所有章节
• 创造生活的12条规则这本书
• 为生活的12条规则创建了章节
• 与本书相关的章节 生活的 12 条规则
• 等等

Answer 1

使用 async await 并使用 let 代替 var 作用域问题

async function seedDb(){
  try{
    await Book.deleteMany({});
    await Chapter.deleteMany({});
    for(let book of books){
      const createdBook = await Book.create(book);
      for(let chapter of chapters){
        if(createdBook.chapters) createdBook.chapters.push(chapter);
        else createdBook.chapters = [chapter];
        await createdBook.save();
      }
    }
  }catch(err){
    console.log(err);
  }
}