<script language="javascript" type="text/javascript"> function Cat(){ } var cat1 = new Cat();//创建类实例 cat1.name = "小狗"; cat1.age = 4; cat1.color="白色"; document.write(cat1.name); document.writeln(cat1.constructor);//实例化后对象，是对象 document.writeln(typeof(cat1)+"<hr />"); document.writeln(Cat.constructor);//原型对象本身也是对象 document.writeln(typeof Cat+"<hr />"); var b="hello";//字符串也是对象 document.writeln(b.constructor);//输出它的构造函数 document.writeln(typeof b+"<hr />"); var c=123;//数值也是对象 document.writeln(c.constructor); document.writeln(typeof c+"<hr />"); </script>

if(cat1 instanceof Cat){//与php的判断方法相同  window.alert("ok"); }