JS匿名函数类生成方式实例分析

<script type="text/javascript">
var Book = (function() {
 // 私有静态属性
 var numOfBooks = 0;
 // 私有静态方法
 function checkIsbn(isbn) {
  if(isbn == undefined || typeof isbn != 'string') {
   return false;
  }
  return true;
 }
 // 返回构造函数
 return function(newIsbn, newTitle, newAuthor) { // implements Publication
  // 私有属性
  var isbn, title, author;
  // 特权方法
  this.getIsbn = function() {
   return isbn;
  };
  this.setIsbn = function(newIsbn) {
   if(!checkIsbn(newIsbn)) throw new Error('Book: Invalid ISBN.');
   isbn = newIsbn;
  };
  this.getTitle = function() {
   return title;
  };
  this.setTitle = function(newTitle) {
   title = newTitle || 'No title specified';
  };
  this.getAuthor = function() {
   return author;
  };
  this.setAuthor = function(newAuthor) {
   author = newAuthor || 'No author specified';
  };
  // 控制对象数目，构造函数
  numOfBooks++; // Keep track of how many Books have been instantiated
         // with the private static attribute.
  if(numOfBooks > 5) throw new Error('Book: Only 5 instances of Book can be '
    + 'created.');
  this.setIsbn(newIsbn);
  this.setTitle(newTitle);
  this.setAuthor(newAuthor);
 }
})();
// 公有静态方法
Book.convertToTitleCase = function(inputString) {
 alert('convertToTitleCase');
};
// 公有非特权方法
Book.prototype = {
 display: function() {
  alert("isbn:"+this.getIsbn()+" title:"+this.getTitle()+" author:"+this.getAuthor());
 }
};
//var theHobbit = new Book(123, '', 'J. R. R. Tolkein'); // 非字符串抛出异常
var theHobbit = new Book('1990-78sd-1092', '', 'J. R. R. Tolkein');
theHobbit.display();
//theHobbit.convertToTitleCase(); // Uncaught TypeError: Object #<Object> has no method 'convertToTitleCase'
Book.convertToTitleCase(); // 输出convertToTitleCase
var theHobbit2 = new Book('1990-78sd-1092', '', 'J. R. R. Tolkein');
theHobbit2.display();
var theHobbit3 = new Book('1990-78sd-1092', '', 'J. R. R. Tolkein');
theHobbit3.display();
var theHobbit4 = new Book('1990-78sd-1092', '', 'J. R. R. Tolkein');
theHobbit4.display();
var theHobbit5 = new Book('1990-78sd-1092', '', 'J. R. R. Tolkein');
theHobbit5.display();
var theHobbit6 = new Book('1990-78sd-1092', '', 'J. R. R. Tolkein');
theHobbit6.display(); // Uncaught Error: Book: Only 5 instances of Book can be created.
</script>