JavaScript 构造器（constructor）介绍

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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>

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