[{"_1":2,"_3":-5,"_4":-5},"loaderData",{"_5":6,"_7":8},"actionData","errors","root",{"_11":-5},"routes/user.$name.replies",{"_9":10,"_11":12,"_13":14,"_15":16,"_17":18,"_19":16},"replies",[35],"user",{"_20":21,"_13":14,"_22":23,"_24":25,"_26":27,"_28":29,"_30":31,"_32":16,"_33":34},"loginname","vincent","page",1,"limit",50,"total","id","31","avatar_url","http://www.gravatar.com/avatar/92987ee35f257bf51576d44f6d456db4?s=48","githubUsername","","create_at","2011-04-12 17:28:16","score",5,"topic_count",0,"reply_count","is_star",false,{"_20":36,"_37":38,"_39":-5,"_40":41,"_42":43,"_44":45,"_46":34,"_47":34,"_32":48,"_49":50,"_26":51,"_52":53},"123","author_id","7","tab","content","只看见了OO就浮想联翩的同学请面壁去。说实在的，为这个题目我纠结了很久，JavaScript中本身一切就是对象（Object），那为什么还要纠结怎样OOP呢？\r\n
\r\n
接yixuan的话题，我先说一个例子。在用NodeJS写程序的过程中，我们常常碰到这样的代码(person.js)：\r\n
\r\n

\r\n
/* vim: set expandtab tabstop=4 shiftwidth=4 foldmethod=marker: */\r\n
\r\n
exports.create  = function(name, age) {\r\n
    var p   = {\r\n
        name    : name,\r\n
        age      : age,\r\n
        echo    : function() {\r\n
            console.log(\"Name: \" + name + \", Age: \" + age);\r\n
        }\r\n
    }\r\n
\r\n
    return p;\r\n
}\r\n

\r\n
\r\n
我们在另一个文件test_class.js中这样使用：\r\n
\r\n

\r\n
var Person     = require('./person.js');\r\n
\r\n
var user        = Person.create('aleafs', 28);\r\n
user.echo();\r\n

\r\n
\r\n
运行test_class.js，不出我们所料，结果如下：\r\n
\r\n

$ node test_class.js\r\n
Name: aleafs, Age: 28\r\n

\r\n
\r\n
如果只求实现功能，我想我们的目的达到了，并且在大多数情况下它能运行得很好。但是，如果创建的person对象很多，我们知道，每一个person对象都要在内存中占用一块地方存放它的echo方法——尽管echo方法对每一个实例都是完全相同的，显然有点浪费对不对？\r\n
\r\n
与上面的代码类似的，person.js还有如下的实现方式：\r\n
\r\n

\r\n
/* vim: set expandtab tabstop=4 shiftwidth=4 foldmethod=marker: */\r\n
\r\n
exports.create  = function(name, age) {\r\n
    this.name   = name;\r\n
    this.age     = age;\r\n
    this.echo   = function() {\r\n
        console.log(\"Name: \" + this.name + \", Age: \" + this.age);\r\n
    }\r\n
}\r\n

\r\n
这样的实现多少想点OOP的程序了，对吧？可是它仍然存在echo方法的内存浪费问题。为此，我们寄希望于prototype机制：\r\n

\r\n
/* vim: set expandtab tabstop=4 shiftwidth=4 foldmethod=marker: */\r\n
\r\n
var Person  = function(name, age) {\r\n
    this.name   = name;\r\n
    this.age    = age;\r\n
}\r\n
\r\n
Person.prototype.echo   = function() {\r\n
    console.log(\"Name: \" + this.name + \", Age: \" + this.age);\r\n
}\r\n
\r\n
exports.create  = Person;\r\n
\r\n

\r\n
由于在JavaScript中，对同一个类的多个对象而言，prototype只被解析并保存一份实例，这个方法确实能够避免我们上面提到的内存浪费问题。但是另一个问题来了，我们对test_class.js原封不动，运行之：\r\n
\r\n
\r\n

$node test_class.js\r\n
node.js:116\r\n
throw e; // process.nextTick error, or 'error' event on first tick\r\n
^\r\n
TypeError: Cannot call method 'echo' of undefined\r\n
at Object. (/home/pengchun/b.js:4:6)\r\n
at Module._compile (module.js:373:26)\r\n
at Object..js (module.js:379:10)\r\n
at Module.load (module.js:305:31)\r\n
at Function._load (module.js:271:10)\r\n
at Array. (module.js:392:10)\r\n
at EventEmitter._tickCallback (node.js:108:26)\r\n

\r\n
什么情况！居然说找不到echo方法！哦，你一定想到了，在test_class.js中我们不能继续使用\r\n
\r\n

\r\n
var user    = Person.create('aleafs', 28);\r\n

\r\n
了，我们得用new创建一个对象，像这样：\r\n
\r\n

\r\n
var user    = new Person.create('aleafs', 28);\r\n

\r\n
\r\n
试了一下，果然能运行了：\r\n

$ node test_class.js\r\n
Name: aleafs, Age: 28\r\n

\r\n
爷爷的，这不是坑爹吗？有没有new并不报语法错误，却在运行时报错。实际上，在上面第二种方法实现person类的情况下也存在这个问题，我们不说了。看看我是怎么解决这个问题的：\r\n

\r\n
/* vim: set expandtab tabstop=4 shiftwidth=4 foldmethod=marker: */\r\n
\r\n
var Person  = function(name, age) {\r\n
    this.name   = name;\r\n
    this.age    = age;\r\n
}\r\n
\r\n
Person.prototype.echo   = function() {\r\n
    console.log(\"Name: \" + this.name + \", Age: \" + this.age);\r\n
}\r\n
\r\n
exports.create  = function(name, age) {\r\n
    return new Person(name, age);\r\n
};\r\n

\r\n
\r\n
看见了没，我仍然采用prototype的方法来定义类。不同的是，我用exports对象指定输出变量时，没有直接把Person类赋值给create，而是创建了一个函数，在这个函数内new了一个对象返回。这样就避免了在外部使用new关键字的问题。\r\n
\r\n
这个方法很好，某某大师也推荐过。我继续推荐这篇文章：\r\n
http://www.ruanyifeng.com/blog/2010/05/object-oriented_javascript_encapsulation.html","title","究竟怎样OOP？","last_reply_at","2014-07-10 08:41:35.416","good","top",13,"visit_count",10733,"2011-03-24 17:35:35","author",{"_13":54,"_22":55},"pengchun","http://www.gravatar.com/avatar/30a95610615ba601ff60c740fa010975?s=48"]