function Person(name,age){
this.name = name;
this.age = age;
if (typeof Person._initialized == "undefined")
{
Person.prototype.displayInfo = function(){
alert("My name is "+this.name+", I'm "+this.age+" years old")
}
Person._initialized = true
}
}
var person1 = new Person("kevin",24); // , displayInfo() 。
var person2 = new Person("Witkey",23); // , 。Person._initialized !=undefined
var person3 = new Person("Andy",25);
person1.displayInfo();
person2.displayInfo();
person3.displayInfo();
/*
Java script , , Person._initialized true, , , Person._initialized undefined。 java script 。
*/