Edit in JSFiddle

// Define the 'Person' Object
function Person() {
    this.sayHello = function () {
        alert('Hello there.');
    };
}

// Define the Student constructor function
function Student() {}

// Inherit from Person
Student.prototype = new Person();

// Correct the constructor pointer, because it points to Person
Student.prototype.constructor = Student;

// Define new properties related to Student Object
Student.prototype.codeWith = function (code) {
    alert('I code with ' + code);
};

var student1 = new Student();
student1.sayHello(); // we can use 'Person' Properties
student1.codeWith('JS'); // and use 'Student' Properties

// change base object implementation for 'sayHello' function
Student.prototype.sayHello = function () {
    alert('hello I am a Student Object');
};
student1.sayHello();