var Book = function( id, title, author, genre, pageCount,publisherID, ISBN, checkoutDate, checkoutMember, dueReturnDate,availability ){
  ...//初始化代码
}
Book.prototype = {
  getTitle:function(){
    return this.title;
  },
  ...
  // 更新借出状态方法
  updateCheckoutStatus:function(bookID, newStatus, checkoutDate,checkoutMember, newReturnDate){...},
  //续借
  extendCheckoutPeriod: function(bookID, newReturnDate){...},
  //是否到期
  isPastDue: function(bookID){...}
} 

 //共享对象
var Book = function(title, author, genre, pageCount, publisherID, ISBN){
  this.title = title;
  this.author = author;
  this.genre = genre;
  this.pageCount = pageCount;
  this.publisherID = publisherID;
  this.ISBN = ISBN;
}; 

 /* Book工厂 单例 */
var BookFactory = (function(){
  var existingBooks = {};
  return{
    createBook: function(title, author, genre,pageCount,publisherID,ISBN){
    /*查找之前是否创建*/
      var existingBook = existingBooks[ISBN];
      if(existingBook){
        return existingBook;
      }else{
        /* 如果没有，就创建一个，然后保存*/
        var book = new Book(title, author, genre,pageCount,publisherID,ISBN);
        existingBooks[ISBN] = book;
        return book;
      }
    }
  }
}); 

 /*BookRecordManager 借书管理类 单例*/
var BookRecordManager = (function(){
  var bookRecordDatabase = {};
  return{
    /*添加借书记录*/
    addBookRecord: function(id, title, author, genre,pageCount,publisherID,ISBN, checkoutDate, checkoutMember, dueReturnDate, availability){
      var book = bookFactory.createBook(title, author, genre,pageCount,publisherID,ISBN);
      bookRecordDatabase[id] ={
        checkoutMember: checkoutMember,
        checkoutDate: checkoutDate,
        dueReturnDate: dueReturnDate,
        availability: availability,
        book: book;
      };
    },
    updateCheckoutStatus: function(bookID, newStatus, checkoutDate, checkoutMember, newReturnDate){
      var record = bookRecordDatabase[bookID];
      record.availability = newStatus;
      record.checkoutDate = checkoutDate;
      record.checkoutMember = checkoutMember;
      record.dueReturnDate = newReturnDate;
    },
    extendCheckoutPeriod: function(bookID, newReturnDate){
      bookRecordDatabase[bookID].dueReturnDate = newReturnDate;
    },
    isPastDue: function(bookID){
      var currentDate = new Date();
      return currentDate.getTime() > Date.parse(bookRecordDatabase[bookID].dueReturnDate);
    }
  };
}); 

 var objectPoolFactory = function (createObjFn) {
  var objectPool = []; //对象池
  return {
    create: function () { //取出
      var obj = objectPool.length === 0 ? createObjFn.apply(this,arguments) : objectPool.shift();
      return obj;
    },
    recover: function (obj) { //收回
      objectPool.push(obj);
    }
  }
}; 

 var iframeFactory = objectPoolFactory(function () {
  var iframe = document.createElement('iframe');
  document.body.appendChild(iframe);
  iframe.onload = function () {
    iframe.onload = null; //防止iframe重复加载的bug
    iframeFactory.recover(iframe); //iframe加载完成后往对象池填回节点(收回)
  };
  return iframe;
});
//调用
var iframe1 = iframeFactory.create();
iframe1.src = 'http://www.qq.com';