get_campaigns.js

getReferrerTraits = function() {
  // Requires: jQuery, jQuery.cookie, segment.io

  // TODO: Update referralHost:blackList with your domain, so we only track external referrers. 

  var analytics_args = [],
      analytics_traits,
      acquisitionSource,
      firstReferrer,
      firstCampaign,
      latestReferrer,
      latestCampaign;
      
      
  // referralHost = the domain name of the referrer of this request, or null
  var referralHost = function() {
    var blackList = ['', null, 'yourdomain.com'];
    var host = document.referrer.toLowerCase().match(/\:\/\/[w\.]*([a-z\-0-9\.]+)\/?/i);
    
    // Break a match out of the array
    host !== null && (host = host[1]);
    
    // Invoke black list
    return (blackList.indexOf(host) > -1) ? null : host;
  } ();

  // Parameter Grabber via http://stackoverflow.com/a/979995/311901 
  var QueryString = function () {
    var query_string = {};
    var query = window.location.search.substring(1);
    var vars = query.split("&");
    for (var i=0;i<vars.length;i++) {
      var pair = vars[i].split("=");
        // If first entry with this name
      if (typeof query_string[pair[0]] === "undefined") {
        query_string[pair[0]] = pair[1];
        // If second entry with this name
      } else if (typeof query_string[pair[0]] === "string") {
        var arr = [ query_string[pair[0]], pair[1] ];
        query_string[pair[0]] = arr;
        // If third or later entry with this name
      } else {
        query_string[pair[0]].push(pair[1]);
      }
    } 
      return query_string;
  } ();

  // log this users' acquisition source:
  //  - utm_source overrides referrer
  //  - Referrer only set when present and not blacklisted
  //  - Directs are not logged. This means the last used referrer will remain. 
  acquisitionSource = (QueryString.utm_source || referralHost);
  if(acquisitionSource !== null) {
    analytics_traits['acquisitionSource'] = acquisitionSource;
  }

  // Get the first and latest campaigns and referrers
  latestReferrer = referralHost;
  latestCampaign = (QueryString.utm_campaign || null);
  firstReferrer  = $.cookie('first_referrer');
  firstCampaign  = $.cookie('first_campaign');

  // Persist the first referer and campaign
  if(firstReferrer == null) {
    firstReferrer = latestReferrer;
    $.cookie('first_referrer', firstReferrer);
  }
  if(firstCampaign == null) {
    firstCampaign = latestCampaign;
    $.cookie('first_campaign', firstCampaign);
  }

  // Append first and latest referrers to the traits being reported with each event
  analytics_traits['firstReferrer'] = firstReferrer;  
  analytics_traits['firstCampaign'] = firstCampaign;  
  analytics_traits['latestReferrer'] = latestReferrer;  
  analytics_traits['latestCampaign'] = latestCampaign;  

  return analytics_traits;
}

patch_identify.js

// After including analytics.js, but before using it anywhere...

// Wrap identify so that all traits persist in a cookie, 
// and each call is merged with previously persisted traits
var identifyFn = analytics['identify'];
analytics['identify'] = function(){
  var new_traits,
      new_arguments = [],
      referrer_traits,
      id,
      old_traits,
      all_traits = {};
      
  // First arg might be the ID, or the attributes may be set anonymously
  if(arguments[0] && (typeof arguments[0] == 'string')){ 
    id = arguments.shift();
  }
  new_traits = arguments[0];
  
  // Collect existing and previous traits together
  old_traits = _.extend({}, JSON.parse($.cookie('analytics_user_traits')));
  all_traits = _.extend({}, old_traits, new_traits);

  // Also collect and merge referrers and campaigns
  referrer_traits = getReferrerTraits();
  all_traits = _.extend({}, all_traits, referrer_traits);

  // Persist traits for next time
  $.cookie("analytics_user_traits", JSON.stringify(all_traits));
  
  // identify the user with all traits to the analytics services
  if(typeof id == 'string') { new_arguments.push(id); }
  new_arguments.push(all_traits);
  identifyFn.apply(identifyFn, new_arguments);
};