Javascript propertyIsEnumerable method usage

 
 
function MyObject() { 
this.name = " I am an instance property "; 
} 
var obj = new MyObject(); 
alert(obj.propertyIsEnumerable("name"));//true 
MyObject.prototype.say = " I am a property of the stereotype "; 
alert(obj.propertyIsEnumerable("say")); //false 
for (var i in obj) { 
alert(i);//name,age 
}