Collecting UTMs and automatic form filling

automatic_utm.js

  (function() {
    function cretaeField(name, value, form) {
      if (value === null) return;
      var input = document.createElement('input');
      input.type = 'hidden';
      input.name = name;
      input.value = value;
      form.appendChild(input);
    }
    const valueExists = (value) => {
          return (value != null && value !== '' && value !== undefined)
    }
    const setValue = (name, value) => {
        sessionStorage.setItem(name, decodeURIComponent(value));
        return value
    }
    const getValue = (name) => sessionStorage.getItem(name) ?? 'n/a';

    function param(name) {
      let params = new URLSearchParams(document.location.search);
      return params.has(name) && valueExists(params.get(name)) ? setValue(name, params.get(name))  : getValue(name );
    }

    var forms = document.querySelectorAll('.lead-form');

    for (var i = 0; i < forms.length; i++) {
      var form = forms[i];
      cretaeField('utm_source', param('utm_source'), form);
      cretaeField('utm_campaign', param('utm_campaign'), form);
      cretaeField('utm_medium', param('utm_medium'), form);
      cretaeField('referral', document.referrer, form);
      cretaeField('_origin', window.location.href, form);
    }
  })();