javascript设计模式--封装和信息隐藏（下）
今天讲解的内容是高级模式（Advanced Patterns），如何实现静态方法和属性，常量还有其他一些知识点。
1.静态方法和属性
其实要实现这一功能还是要借助于闭包。在上一讲中的第三种实现方式也使用了闭包，但通过那种实现，内部属性和方法是实例级别的。
var Book = (function() { // Private static attributes. var numOfBooks = 0; // Private static method. function checkIsbn(isbn) { ... } // Return the constructor. return function(newIsbn, newTitle, newAuthor) { // implements Publication // Private attributes. var isbn, title, author; // Privileged methods. 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'; }; this.getNumOfBooks = function(){ return numOfBooks; }; // Constructor code. numOfBooks++; // Keep track of how many Books have been instantiated // with the private static attribute. if(numOfBooks > 50) throw new Error('Book: Only 50 instances of Book can be ' + 'created.'); this.setIsbn(newIsbn); this.setTitle(newTitle); this.setAuthor(newAuthor); }})();// Public static method.Book.convertToTitleCase = function(inputString) { ...};// Public, non-privileged methods.Book.prototype = { display: function() { ... }};对匿名函数不了解的同学可以自己去查阅相关资料。其实上面的代码等价于:代码2
var tempBook = function() { // Private static attributes. var numOfBooks = 0; // Private static method. function checkIsbn(isbn) { ... } // Return the constructor. return function(newIsbn, newTitle, newAuthor) { // implements Publication ... }};var Book = tempBook();// Public static method.Book.convertToTitleCase = function(inputString) { ...}; // Public, non-privileged methods.Book.prototype = { display: function() { ... }};那么如果再执行之前的代码会有什么效果呢：