JavaScript 构造器（constructor）介绍
JavaScript构造器（constructor）是对象的一个属性，为只读 ，主要用途有：
1、可以用来判断某对象是否由某个函数（类）实例化得来；
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>constructor</title>
</head>
<body>
<script lang="javascript">
var ClassA = function(){
this.name = "Zhangsan";
var age = 40;
}
ClassA.prototype.url = "http://localhost:9080/myweb";
var obj = new ClassA();
obj.url = "http://www.baidu.com";
obj.name = "Lisi";
if(obj.constructor == ClassA){
alert('Object obj2 initialized by ClassA!');
}
</script>
</body>
</html>2、获取对象的构造函数，可以重复利用其来实例化同类的对象：
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>constructor</title>
</head>
<body>
<script lang="javascript">
var ClassA = function(){
this.name = "Zhangsan";
var age = 40;
}
ClassA.prototype.url = "http://localhost:9080/myweb";
var obj = new ClassA();
obj.url = "http://www.baidu.com";
obj.name = "Lisi";
alert('obj.url:' + obj.url + ',prototype.url:' + ClassA.prototype.url + ',name:' + obj.name + ',age:' + obj.age
+ ',constructor :' + obj.constructor );
var obj2 = new obj.constructor();
alert(obj2.name);
</script>
</body>
</html>
