common.js

function Common() {
let self = this;
/* Properties */
this.promoBar = {
    promoItems: null,
    currentItem: 0,
    numberOfItems: 0,
};
/* Methods */
this.initialisePromo = function () {
    /* Get all items in promo bar */
    let promoItems = $("#promo > div");
    /* Set values */
    this.promoBar.promoItems = promoItems;
    this.promoBar.numberOfItems = promoItems.length;
    /* Initiate promo loop to show next item */
    this.startDelay();
}
this.startDelay = function () {
    /* Wait 4 seconds then show the next message */
    setTimeout(function () {
        self.showNextPromoItem()
    }, 4000);
}
this.showNextPromoItem = function () {
    /* Fade out the current item */
    $(self.promoBar.promoItems).fadeOut("slow").promise().done(function () {
        /* Increment current promo item counter */
        if (self.promoBar.currentItem >= (self.promoBar.numberOfItems - 1)) {
            /* Reset counter to zero */
            self.promoBar.currentItem = 0;
        } else {
            /* Increase counter by 1 */
            self.promoBar.currentItem++;
        }
        /* Fade in the next item */
        $(self.promoBar.promoItems).eq(self.promoBar.currentItem).fadeIn("slow", function () {
            /* Delay before showing next item */
            self.startDelay();
        });
    });
}
}

$(document).ready(function () {
    /* Instantiate new Common class */
    app.Common = new Common();
    /* Initialize the Promo bar */
    app.Common.initialisePromo();
});