observer.js

function Observer() {
    this.observerContainer = [];
}

Observer.prototype.subscribe = function (element) {
    this.observerContainer.push(element);
}

/**
 * removes an element from the container
 */
Observer.prototype.unsubscribe = function (element) {

    const elementIndex = this.observerContainer.indexOf(element);
    if (elementIndex > -1) {
        this.observerContainer.splice(elementIndex, 1);
    }
}

/**
 * notifies all the element added to the container by calling 
 * each subscribed components added to the container
 */
Observer.prototype.notifyAll = function (element) {
    this.observerContainer.forEach(function (observerElement) {
        observerElement(element);
    });
}