构造器的拷贝功能（对象应该有一个创建自身的方法）

<script>
    var a = function (name, age) {

        this.name = name;
        this.age = age;
        this.clone = function () {
            return new a;
        }
    }

    var aa = new a;
    aa.name = "zz";
    aa.age = "5";
    alert(aa.age);

    var aaa = aa.clone();
    aaa.name = "123";
    alert(aaa.name);
</script>