oop.js

// Helper for implementing mixins.
function mixin(dest) {
    for (var i = 1; i < arguments.length; i++) {
        var source = arguments[i];
        for (var prop in source) {
            if (!dest[prop]) {
                dest[prop] = source[prop];
            }
        }
    }
}

// Template for writing a basic class
// Here the constructor takes the arguments `firstName` and `lastName`
function Person(firstName, lastName) {
    // createdAt is analogous to private variable
    var createdAt = new Date();

     
    // These are public.
    this.firstName = firstName;
    this.lastName = lastName;

    // The variable `createdAt` can't be accessed without this accessor
    this.createdAt = function() {
        return createdAt;
    }
}

// Your usual method.
Person.prototype.getName = function() {
    return this.lastName + ", " + this.firstName;
}

// This is a mixin
function Serializable() {}
Serializable.prototype = {
    serialize: function() {
        print("Serializing " + this.getName());
    }
}

// Now Person is Serializable. The properties of mixin Serializable are 
// mixed into person.
mixin(Person.prototype, Serializable.prototype);


// This is an example of inheritance.
function User(firstName, lastName, password) {
    this.password = password;
    // JS doesn't have a super() way of calling parent constructor.
    // This will just call constructor. The prototype will have to be inherited later.
    Person.call(this, firstName, lastName);
}

// Inherit from Person
User.prototype = Object.create(Person.prototype);
// Add method unique to Person.
User.prototype.getPassword = function() {
    return this.password;
}

// Override method.
User.prototype.getName = function() {
    // We aren't actually overriding anything but just calling super method.
    return Person.prototype.getName.call(this);
}

// Another mixin.
// Mixins can be object literals(and generally are).
var Authorizable = {
    authorize: function() {
        print("Authorizing " + this.getName());
    }
}


mixin(User.prototype, Authorizable);

// Demo
var user = new User("Rahul", "Kumar", "test");
print(user.getName());
print(user.createdAt());
user.serialize();
user.authorize();