Callback hell

HTML

<!-- status details -->
<script src="https://raw.githubusercontent.com/kriskowal/q/v1/q.js"></script>
<div class="statList">
    <div class="statList__item">
        <div class="status">
            <div class="status__title">Tweets</div>
            <div class="status__count totalTweets"></div>
        </div>
    </div>
    <div class="statList__item">
        <div class="status">
            <div class="status__title">Photos</div>
            <div class="status__count totalPhotos"></div>
        </div>
    </div>
    <div class="statList__item">
        <div class="status">
            <div class="status__title">Favourites</div>
            <div class="status__count totalFavourites"></div>
        </div>
    </div>
</div>
<!-- tweet timeline -->
<div class="tweetFeed">
    <div class="timeLine"></div>
</div>

CSS

body {
    background: #f5f8fa;
    font: 16px/22px Arial, sans-serif;
    margin: 0;
}
.statList {
    background: #fff;
    border-bottom: 1px solid #e1e8ed;
    height: 60px;
    overflow: hidden;
}
.statList__item {
    float: left;
    width: 75px;
    height: 60px;
    display: table;
}
.status {
    display: table-cell;
    text-align: center;
    text-transform: uppercase;
    vertical-align: middle;
}
.status__title {
    color: #66757f;
    font-size: 11px;
    letter-spacing: .02em;
    text-transform: uppercase;
}
.status__count {
    color: #C29A34;
    font-size: 18px;
    font-weight: 500;
    padding-top: 3px;
}
.tweetFeed {
    margin: 10px;
}
.tweet {
    background: #fff;
    border: 1px solid #e1e8ed;
    padding: 15px;
}
.tweet:nth-child(1) {
    border-radius: 5px 5px 0 0;
}
.tweet:nth-child(n+2) {
    border-top: none;
}
.tweet__name {
    color: #292f33;
    display: inline-block;
    font-size: 14px;
    font-weight: bold;
}
.tweet__handle {
    color: #8899a6;
    display: inline-block;
    font-size: 13px;
    margin-left: 10px;
}
.tweet__message {
    margin-top: 5px;
}

JavaScript

(function () {
    var timeLine = document.querySelector('.timeLine');
    var totalTweets = [];

    /**
     * get
     *
     * Tiny utility for making XHR requests
     * @param  {String}   url
     * @param  {Function} callback [description]
     */

    function get(url, callback, errback) {
        var req = new XMLHttpRequest();
        req.open('GET', url, true);
        req.onreadystatechange = function () {
            if (req.readyState != 4) return;
            if (req.status === 200) {
                callback(req);
            } else {
                errback(req);
            }
        };
        req.send(null);
    }


    /**
     * Asynch Requests
     * Nest callback grossness
     */

    function errorMessageHandler(err) {
        onError(err);
    }

    function fourthLevelHandler(data) {
        var deferred = Q.defer(); 
        totalTweets.push(data.response);
        showStats();
        return deferred.promise; 
    }

    function thirdLevelHandler(data) {
        var deferred = Q.defer(); 
        totalTweets.push(data.response);
        // our third async req
        get('https://api.myjson.com/bins/29e3f',
        deferred.resolve,
        deferred.reject);
        return deferred.promise; 
    }

    function secondLevelHandler(data) {
        var deferred = Q.defer(); 
        get('https://api.myjson.com/bins/3zjqz',
        deferred.resolve,
        deferred.reject);
        return deferred.promise; 
    }

    function firstLevelHandler(data) {
        var deferred = Q.defer(); 
        totalTweets.push(data.response);
        // our second async req wrapped in a 2 second delay
        setTimeout(deferred.resolve, 2000);
        return deferred.promise; 

    }
    // our first async req
    function initiallCall() {
        var deferred = Q.defer(); 
        get('https://api.myjson.com/bins/2qjdn',
        deferred.resolve,
        deferred.reject);
        return deferred.promise; 
    }

    initiallCall()
       ...