从零开始的毕设--JavaScript-prototype对象

方法过载

上一节，我们在构造函数里利用this关键字创建blog对象的方法。但是根据这个创建的每个blog对象，均各有一份对象方法的副本！浪费！

方法应该为各个对象所共享。

共享方法

多亏了每个对象有个隐藏对象prototype(它以特性的形式存在)，JavaScript的类才能成真。prototype对象用于设定隶属于类层的特性与方法，而非属于实例的！
所以，使用prototype对象，即可创建类拥有的方法。
不用再放在构造函数里，放在外部。

  // Blog object constructor
      function Blog(body, date) {
        // Assign the properties
        this.body = body;
        this.date = date;
      }

      // Return a string representation of the blog entry
      Blog.prototype.toString = function() {
        return "[" + (this.date.getMonth() + 1) + "/" + this.date.getDate() + "/" +
          this.date.getFullYear() + "] " + this.body;
      };

      // Return a formatted HTML representation of the blog entry
      Blog.prototype.toHTML = function(highlight) {
        // Use a gray background as a highlight, if specified
        var blogHTML = "";
        blogHTML += highlight ? "<p style='background-color:#EEEEEE'>" : "<p>";

        // Generate the formatted blog HTML code
        blogHTML += "<strong>" + (this.date.getMonth() + 1) + "/" + this.date.getDate() + "/" +
          this.date.getFullYear() + "</strong><br />" + this.body + "</p>";
        return blogHTML;
      };

      // See if the blog body contains a string of text
      Blog.prototype.containsText = function(text) {
        return (this.body.toLowerCase().indexOf(text.toLowerCase()) != -1);
      };

共享属性

就像Java里的static 属性，每个实例都是共享这个属性的。事实上，我们也使用prototype创建属性即可。

blog.prototype.signature="Puzzler Ruby";

扩展标准对象

扩展对象的关键就是prototype对象，因为每一个javascript对象里都有它，所以扩展任何对象，只需要把特性和方法加入它的prototype对象里，借以建立类特性和类拥有的方法。
假如我们要扩展String对象，我们使用如下代码：

String.prototype.scramble=function(){
	//return scrambled string
}

我们要使用这个scramble()方法，只需要在字符串变量处调用即可：

alert(this.signature.scramble());

同理，假如要使用Date对象，因为Date.toString()方法返回的字符串不尽如人意，所以我们加入新方法即可。

Date.prototype.shortFormat = function() {
        return (this.getMonth() + 1) + "/" + this.getDate() + "/" + this.getFullYear();
      }
      /** this.date.shortFormat()调用*/

再看构造函数

function Blog(body, date, image) {
        // Assign the properties
        this.body = body;
        this.date = date;
        this.image = image;
      }
Blog.prototype.toHTML = function(highlight) {
        // Use a gray background as a highlight, if specified
        var blogHTML = "";
        blogHTML += highlight ? "<p style='background-color:#EEEEEE'>" : "<p>";

        // Generate the formatted blog HTML code
        if (this.image) {
          blogHTML += "<strong>" + this.date.shortFormat() + "</strong><br /><table><tr><td><img src='" +
            this.image + "'/></td><td style='vertical-align:top'>" + this.body + "</td></tr></table><em>" +
            this.signature + "</em></p>";
        }
        else {
          blogHTML += "<strong>" + this.date.shortFormat() + "</strong><br />" + this.body +
            "<br /><em>" + this.signature + "</em></p>";
        }
        return blogHTML;
      };
  var blog = [ new Blog("Got the new cube I ordered. It's a real pearl.", new Date("08/14/2008")),
                   new Blog("Solved the new cube but of course, now I'm bored and shopping for a new one.", new Date("08/19/2008")),
                   new Blog("Managed to get a headache toiling over the new cube. Gotta nap.", new Date("08/16/2008")),
                   new Blog("Found a 7x7x7 cube for sale online. Yikes! That one could be a beast.", new Date("08/21/2008")),
                   new Blog("Met up with some fellow cubers to discuss the prospect of a 7x7x7 cube. Mixed feelings.", new Date("08/29/2008")),
                   new Blog("Went ahead and ordered the scary 7x7x7 cube. Starting a mental exercise regimen to prepare.", new Date("09/01/2008")),
                   new Blog("Attended a rally outside of a local toy store that stopped carrying cube puzzles. Power to the puzzlers!", new Date("09/03/2008")),
                   new Blog("Got the new 7x7x7 cube. Could be my last blog post for a while...", new Date("09/05/2008")),
                   new Blog("Wow, it took me a couple of weeks but the new cube is finally solved!", new Date("09/19/2008"), "cube777.png") ];
      

由上述3段可知，构造函数传参可以不传全部，没有的部分为空。