JavaScript OOP Design Pattern - Observer Pattern

ObserverPattern.js

//observer pattern

//convert Subject into constructor function as there can be more than 1
var Subject = function () {
    var observerCollection = [],
        subject = {
            "registerObservers": function ( observerArr ) {
                observerArr.forEach( addToRegister );
                return true;
            },
            "unregisterObserver": function ( observer ) {
                observerCollection.splice( observer.getID(), 1 );
                return true;
            },
            "notify": function () {
                observerCollection.forEach( fireNotify );
            }
        },
        addToRegister = function ( subscriber, i ) {
            assignID( subscriber, observerCollection.length );//added here to assign 0
            observerCollection.push( subscriber );
        },
        assignID = function ( o, id ) {
            o.addID( id );
        },
        fireNotify = function ( observer, i ) {
            observer.notify();
        };
    return subject;
};

//constructor pattern used over revealing module pattern as there will be
//N instances of observers
function Observer () {
    this.addID = function ( id ) {
        if ( ! this._id ) {
            this._id = id;
            return true;
        }
    };
    this.getID = function () {
        if ( this._id ) {
            return this._id;
        }
    };
    this.notify = function () {
    };
}

var subject = Subject(),
    observer1 = new Observer(),
    observer2 = new Observer(),
    observer3 = new Observer(),
    observer4 = new Observer();

//concrete notify() implementations
observer1.notify = function () {
    console.log( "1" );
};

observer2.notify = function () {
    console.log( "2" );
};

observer3.notify = function () {
    console.log( "3" );
};

observer4.notify = function () {
    console.log( "4" );
};

//register subscribers/observers
subject.registerObservers( [ observer1, observer2, observer3, observer4 ] );

//fire notification w/ observer #3
subject.notify();

//unregister observer #3
subject.unregisterObserver( observer3 );

//fire notification w/o observer #3
subject.notify();