// define the Person Class
function Person() {}
Person.prototype.walk = function(){
 alert ('I am walking!');
};
Person.prototype.sayHello = function(){
 alert ('hello');
};
// define the Student class
function Student() {
 // Call the parent constructor
 Person.call(this);
}
// inherit Person
Student.prototype = new Person();
// correct the constructor pointer because it points to Person
Student.prototype.constructor = Student;
// replace the sayHello method
Student.prototype.sayHello = function(){
 alert('hi, I am a student');
}
// add sayGoodBye method
Student.prototype.sayGoodBye = function(){
 alert('goodBye');
}
var student = new Student();
student.sayHello();
student.walk();
student.sayGoodBye();
// check inheritance
alert(student instanceof Person); // true 
alert(student instanceof Student); // true