Tracking Salesforce UTM Paramaters across pages

utm-tracking.js

(function () {
  function getParameterByName(name, url) {
      if (!url) url = window.location.href;
      name = name.replace(/[\[\]]/g, "\\$&");
      var regex = new RegExp("[?&]" + name + "(=([^&#]*)|&|#|$)"),
          results = regex.exec(url);
      if (!results) return null;
      if (!results[2]) return '';
      return decodeURIComponent(results[2].replace(/\+/g, " "));
  }
  
  var campaignId = getParameterByName('C_SFDCLastCampaignID');
  
  if (campaignId) {
    localStorage.setItem('C_SFDCLastCampaignID', campaignId);
  } else {
    campaignId = localStorage.getItem('C_SFDCLastCampaignID');
  }
  
  if (campaignId) {
    var C_SFDCLastCampaignIDFields = document.getElementsByClassName('C_SFDCLastCampaignID');
    if (C_SFDCLastCampaignIDFields.length) {
      Array.prototype.forEach.call(C_SFDCLastCampaignIDFields, function (field) {
        field.value = campaignId;
      });
    }
  }
})();