Function.prototype.extend for simple classes in ES5

lib.js

Object.getOwnPropertyDescriptors = function getOwnPropertyDescriptors(obj) {
    var descriptors = {};
    for (var prop in obj) {
        if (obj.hasOwnProperty(prop)) {
            descriptors[prop] = Object.getOwnPropertyDescriptor(obj, prop);
        }
    }
    return descriptors;
};

Function.prototype.extend = function extend(proto) {
    var superclass = this;
    var constructor;

    if (!proto.hasOwnProperty('constructor')) {
        Object.defineProperty(proto, 'constructor', {
            value: function () {
                // Default call to superclass as in maxmin classes
                superclass.apply(this, arguments);
            },
            writable: true,
            configurable: true,
            enumerable: false
        });
    }
    constructor = proto.constructor;
    
    constructor.prototype = Object.create(this.prototype, Object.getOwnPropertyDescriptors(proto));
    
    return constructor;
};

test.js

// Object is a function, so it gets extend()
// That means Object.extend() creates a new constructor function
// with .prototype.__proto__ === Object.prototype
var Person = Object.extend({
    constructor: function Person(name) {
        this.name = name;
    },
    say: function (message) {
        return this.name + ' says: ' + message;
    }
});

var Pirate = Person.extend({
    say: function (message) {
        //lack of super makes this very verbose :(
        return 'Capt\'n ' + Object.getPrototypeOf(Pirate.prototype).say.apply(this, arguments) + ' arrr!';
    }
});

var blackbeard = new Pirate('Blackbeard');
console.log(blackbeard);
console.log(blackbeard.say('ahoy!'));