Parse UTM codes to Contact Form 7 by javascript

parse_utm_codes_by_JS.js

/**
 * Solving  a trouble with WP Engine which is caching website without URL parameters and re-attaches them back once the request is compiled.
 * If you need to add UTM values to any form (not only CF7) you can use this JS snippet on the form page.
 *
 * Author: Karolína Vyskočilová (karolina@kybernaut.cz)
 * Author website: https://kybernaut.cz
 * Date created: 2020-11-13
 *
 * Read more about WP Engine's cache:  https://wpengine.com/support/utm-gclid-variables-caching/
 */

(function() {
   var urlParams = new URLSearchParams(window.location.search);
   var paramNames = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_content'];
   for ( var i = 0, length = paramNames.length; i < length; i ++ ) {
     if ( urlParams.get(paramNames[i])) {
         document.querySelector('.wpcf7-hidden[name="'+paramNames[i]+'"]').value = urlParams.get(paramNames[i]);
     }
   }
})();