UTM and Referral Cookie - Find more here https://github.com/arturmamedov/utm_referral-cookie

traffic_sources_cookies.js

/** 
 * You also can find
 * Improved version and documentation
 * on repository: https://github.com/arturmamedov/utm_referral-cookie
*/

// configuration
var $hostname = '.sviluppo1.loc',
    cookie_params = ['source', 'medium', 'campaign']; // there are also [... 'term', 'content'] !commented

function crumbleCookie(a) {
    for (var d = document.cookie.split(";"), c = {}, b = 0; b < d.length; b++) {
        var e = d[b].substring(0, d[b].indexOf("=")).trim(),
            i = d[b].substring(d[b].indexOf("=") + 1, d[b].length).trim();
        c[e] = i;
    }
    if (a) return c[a] ? c[a] : null;
    return c;
}

function bakeCookie(a, d, c, b, e, i) {
    var j = new Date();
    j.setTime(j.getTime());
    c && (c *= 864E5);
    j = new Date(j.getTime() + c);
    document.cookie = a + "=" + escape(d) + (c ? ";expires=" + j.toGMTString() : "") + (b ? ";path=" + b : "") + (e ? ";domain=" + e : "") + (i ? ";secure" : "");
}

/**
 * Write cookie as url string
 * use getTrafficSource() and bakeCookie()
 *
 * @param n Name of cookie to write
 *
 * @return void
 */
function writeLogic(n) {
    var a = getTrafficSource(n, $hostname);

    a = a.replace(/\|{2,}/g, "|");
    a = a.replace(/^\|/, "");
    a = unescape(a);

    bakeCookie(n, a, 182, "/", "", ""); //Cookie expiration sets to 182 days
}

/**
 * Read cookie saved as url and return object with key=>value
 *
 * @param n Name of cookie to read
 *
 * @returns object key=>value object of cookie
 */
function readLogic(n) {
    var cookie_string = crumbleCookie()[n], cookie_obj = {}, param;

    for (var key in cookie_params) {
        param = cookie_params[key];
        cookie_obj[param] = getParam('?' + decodeURIComponent(cookie_string), param);
    }

    return cookie_obj;
}


/**
 * Get Formatted string of cookie Referral
 *
 * @param cookie_obj Object with cookie referral params {source, medium, campaign}
 *
 * @return string Formatted string of Referral
 */
function attrToString(cookie_obj) {
    if (cookie_obj.source == 'direct') {
        return 'direct';
    } else {
        // open with brackets
        var attr_value = cookie_obj.source + '(' + cookie_obj.medium;

        // add campaign name if exist
        if (cookie_obj.campaign.length > 1) {
            attr_value = attr_value + ' | ' + cookie_obj.campaign;
        }

        // close brackets
        attr_value = attr_value + ')';
    }

    // return string
    return attr_value;
}

/**
 * Get value of url query string param "?param=value"
 *
 * @param s Url query string "?parma=value"
 * @param q The param to retrieve
 *
 * @return {string} param value
 */
function getParam(s, q) {
    try {
        var match = s.match('[?&]' + q + '=([^&]+)');
        return match ? match[1] : '';
        // return s.match(RegExp('(^|&)'+q+'=([^&]*)'))[2];
    } catch(e) {
        return '';
    }
}

function calculateTrafficSource() {
    var source='', medium='', campaign=''; //, term='', content='';
    var search_engines = [['bing', 'q'], ['google', 'q'], ['yahoo', 'q'], ['baidu', 'q'], ['yandex', 'q'], ['ask', 'q'], ['libero.it', 'qs'], ['virgilio.it', 'q']]; //List of search engines
    var socials = [['facebook'], ['twitter'], ['instagram'], ['flickr'], ['tumblr'], ['vimeo'], ['pinterest']]; // List of socials ['plus.google'], ['plus.url.google'],
    var ref = document.referrer;
    ref = ref.substr(ref.indexOf('//')+2);
    var ref_domain = ref;
        // ref_path = '/', no need
        // ref_search = ''; no need

    // Checks for campaign parameters
    var url_search = document.location.search;

    // console.log(url_search.indexOf('utm_source'));
    // console.log(getParam(url_search, 'gclid'));
    // console.log(url_search);

    if(url_search.indexOf('utm_source') > -1) {
        source   = getParam(url_search, 'utm_source');
        medium   = getParam(url_search, 'utm_medium');
        campaign = getParam(url_search, 'utm_campaign');
        // term     = getParam(url_search, 'utm_term'); no need
        // content  = getParam(url_search, 'utm_content'); no need
    }
    else if (getParam(url_search, 'gclid')) {
        source = 'google';
        medium = 'cpc';
        campaign = 'gclid';
    }
    else if(ref) {
        // separate domain, path and query parameters
        if (ref.indexOf('/') > -1) {
            ref_domain = ref.substr(0,ref.indexOf('/'));
            // ref_path = ref.substr(ref.indexOf('/')); no need
            /* no need if (ref_path.indexOf('?') > -1) {
                ref_search = ref_path.substr(ref_path.indexOf('?')+1);
                ref_path = ref_path.substr(0, ref_path.indexOf('?'));
            }*/
        }
        medium = 'referral';
        source = ref_domain;
        // Extract term for organic source
        for (var i=0; i<search_engines.length; i++){
            if(ref_domain.indexOf(search_engines[i][0]) > -1){
                medium = 'organic';
                source = search_engines[i][0];
                // term = getParam(ref_search, search_engines[i][1]) || '(not provided)'; no need
                break;
            }
        }
        // Or of social
        for (var i=0; i<socials.length; i++){
            if (ref_domain.indexOf(socials[i][0]) > -1) {
                medium = 'social';
                source = socials[i][0];
                break;
            }
        }
    }

    return {
        'source'  : source,
        'medium'  : medium,
        'campaign': campaign
    }; // 'term'    : term, 'content' : content
}

function getTrafficSource(cookieName, hostname) {
    var trafficSources = calculateTrafficSource();
    var source = trafficSources.source.length === 0 ? 'direct' : trafficSources.source;
    var medium = trafficSources.medium.length === 0 ? 'none' : trafficSources.medium;
    var campaign = trafficSources.campaign.length === 0 ? 'direct' : trafficSources.campaign;
    // exception
    if(medium === 'referral') {
        campaign = '';
    }
    // var rightNow = new Date(); no need date
    var value = 'source='   + source +
        '&medium='  + medium +
        '&campaign='+ campaign;
    // '&term='    + trafficSources.term +
    // '&content=' + trafficSources.content +
    // + '&date='    + rightNow.toISOString().slice(0,10).replace(/-/g,""); no need date
    return value;
}

// Self-invoking function
(function(){
    // no need date
    // var date = new Date();
    // var fr_date = date.getUTCFullYear().toString() + ((date.getUTCMonth() < 9) ? '0' + (date.getUTCMonth()+1).toString() : (date.getUTCMonth()+1).toString()) + ((date.getUTCDate() < 10) ? '0' + date.getUTCDate().toString() : date.getUTCDate().toString());

    var session = crumbleCookie()['js_referral'];

    // First time session
    if (typeof session == 'undefined')
    {
        writeLogic('js_referral');
    } else {
        writeLogic('js_referral_returned');
    }
})();

var session = readLogic('js_referral'),
    session2 = readLogic('js_referral_returned');

// First time session (only the first time visit)
if (typeof session != 'undefined') {
    console.log(session); // object {source, medium, campaign}
    console.info(attrToString(session)); // or formatted string "source (medium | campaign)"
}
// Last time session (ever the last time visit)
if (typeof session2 != 'undefined') {
    console.info(session2); // object {source, medium, campaign}
    console.info(attrToString(session2)); // or formatted string "source (medium | campaign)"
}

Hey man, I liked your code and it helped, but I found a problem when my traffic comes from a search engine and the session object is created as undefined.

The error is the following:
Uncaught TypeError: Cannot read property '0' of undefined at calculateTrafficSource (<anonymous>:5:215) at getTrafficSource (<anonymous>:6:38) at writeLogic (<anonymous>:2:275) at <anonymous>:6:366 at <anonymous>:6:402 at gtm.js?id=GTM-NNBV69J&gtm_cookies_win=x:646 at Object.c [as __html] (gtm.js?id=GTM-NNBV69J&gtm_cookies_win=x:648) at Ub (gtm.js?id=GTM-NNBV69J&gtm_cookies_win=x:541) at g (gtm.js?id=GTM-NNBV69J&gtm_cookies_win=x:575) at gtm.js?id=GTM-NNBV69J&gtm_cookies_win=x:526

In line 156, have a error. Correct is "for (var i=0; i<socials.length; i++){"

@JhonathaNunes thanks, strange error, maybe is for error that found @morojosa i now fix it. Also i create repository with documentation of this code https://github.com/arturmamedov/utm_referral-cookie