store_click_id_as_cookie.html

<script>
//   Store any click ID discovered in the query params as a cookie value.
function getCookie(name) {
  var match = document.cookie.match(new RegExp('(^| )' + name + '=([^;]+)'));
  if (match) return match[2];
  else return null;
}

function setCookie(name, value, days) {
  var existingValue = getCookie(name);
  
  // Check if the cookie already exists or the value to be set is not defined or empty
  if (existingValue || !value) {
    return;
  }
  
  var expires = "";
  if (days) {
    var date = new Date();
    date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
    expires = "; expires=" + date.toUTCString();
  }
  document.cookie = name + "=" + (value || "") + expires + "; path=/";
}

function getURLParameter(paramName) {
  var regex = new RegExp('[?&]' + paramName + '(=([^&#]*)|&|#|$)'),
      results = regex.exec(window.location.href);
  if (!results) return null;
  if (!results[2]) return '';
  return decodeURIComponent(results[2].replace(/\+/g, ' '));
}

// Click ID names and their corresponding parameters
var clickIDs = ["gclid", "wbraid", "gbraid", "fbclid", "msclkid"];

// Set cookies for each URL parameter
clickIDs.forEach(function(clickID) {
  var value = getURLParameter(clickID);
  setCookie(clickID, value, 30);
});

</script>