设计模式（十一）：享元模式

// 每种书的数据，作为共享数据。
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;
};
 
// 书籍单例，获取共享数据（书籍）的方法。
var BookFactory = (function () {
  var existingBooks = {}, existingBook;
  return {
    createBook: function ( title, author, genre, pageCount, publisherID, ISBN ) {
 
      existingBook = existingBooks[ISBN];
      if ( !!existingBook ) {
        return existingBook;
      } else {
        var book = new Book( title, author, genre, pageCount, publisherID, ISBN );
        existingBooks[ISBN] = book;
        return book;
      }
    }
  };
})();
 
//书籍记录管理器单例
var BookRecordManager = (function () {
  var bookRecordDatabase = {};
  return {
    //添加新书
    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 );
    }
  };
})();

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var stateManager = {
  fly: function () {
    var self = this;
    $( "#container" )
          .unbind()
          .on( "click", "div.toggle", function ( e ) {
            self.handleClick( e.target );
          });
  },
  handleClick: function ( elem ) {
    elem.find( "span" ).toggle( "slow" );
  }
};