Save the UTM parameteres in localStorage for a month

saveUTMParameters.js

function saveUTMParameters() {
  var params = Object.fromEntries(new URLSearchParams(document.location.search));
  
  // utm_campaign exists
  if (Object(params).hasOwnProperty('utm_campaign')) {
    var date = new Date();
    var expires_date = new Date(date);
    expires_date.setMonth(date.getMonth() - 1);
    
    // get current utm history or create empty array
    var utm_history = JSON.parse(localStorage.getItem('utm_history')) || [];
    if (utm_history.length > 0) {
      var last_object = Object.assign({}, utm_history.slice(-1)[0]);
      delete last_object.created_at;
      
      // don't update if last object equal the new object
      if (JSON.stringify(last_object) === JSON.stringify(params)) {
        return false;
      }
    }
    
    // add new object to the array after the created_at
    Object.assign(params, { created_at: date.toISOString() });
    utm_history.push(params);
    
    // prepared unexpired data
    var unexpired_utm_history = utm_history.filter(function(obj) => {
      return obj.created_at >= expires_date.toISOString();
    });
    
    localStorage.setItem('utm_history', JSON.stringify(unexpired_utm_history));
  }
}
window.addEventListener('load', saveUTMParameters);