Gravity Forms | Log a parameter value to local storage and send with Gravity Form entry, such as Google Ads GCLID or other params

gravity-forms-gclid-params-on-submit.js

// get parameters of URL
function getParam(p) {
	var match = RegExp('[?&]' + p + '=([^&]*)').exec(window.location.search);
	return match && decodeURIComponent(match[1].replace(/\+/g, ' '));
}
// set expiration date
function getExpiryRecord(value) {
	var expiryPeriod = 90 * 24 * 60 * 60 * 1000; // 90 day expiry in milliseconds

	var expiryDate = new Date().getTime() + expiryPeriod;
	return {
		value: value,
		expiryDate: expiryDate
	};
}
// get desired param (gclid), specify the form field id to add it to, add it to local storage, and set the value in the form field
function addGclid() {
	var gclidParam = getParam('gclid'); // what param to get
	var gclidFormFields = ['input_6_16']; // all possible gclid form field ids here, e.g., ['gclid_field', 'foobar']
	var gclidRecord = null;
	var currGclidFormField;

	var gclsrcParam = getParam('gclsrc'); //gclsrc param indicates the source of the click ID, but can also be empty
	var isGclsrcValid = !gclsrcParam || gclsrcParam.indexOf('aw') !== -1;

	gclidFormFields.forEach(function (field) {
		if (document.getElementById(field)) {
			currGclidFormField = document.getElementById(field);
		}
	});

	if (gclidParam && isGclsrcValid) {
		gclidRecord = getExpiryRecord(gclidParam);
		localStorage.setItem('gclid', JSON.stringify(gclidRecord));
	}

	var gclid = gclidRecord || JSON.parse(localStorage.getItem('gclid'));
	var isGclidValid = gclid && new Date().getTime() < gclid.expiryDate;

	if (currGclidFormField && isGclidValid) {
		currGclidFormField.value = gclid.value;
	}
}
window.addEventListener('load', addGclid);


// get desired param (device), which we set via the Google Ads ValueTrack parameters, then specify the form field id to add it to, add it to local storage, and set the value in the form field
function addAdsDevice() {
	var adsDeviceParam = getParam('device'); // what param to get
	var adsDeviceFormFields = ['input_6_21']; // form field to put the param value
	var adsDeviceRecord = null; // set the local storage record as null to start
	var currAdsDeviceFormField;

	// for each input field  we specified
	adsDeviceFormFields.forEach(function (field) {
		if (document.getElementById(field)) {
			currAdsDeviceFormField = document.getElementById(field); // get the desired input field(s)
		}
	});

	// if the parameter existed
	if (adsDeviceParam) {
		adsDeviceRecord = getExpiryRecord(adsDeviceParam); // get the desired expiration date that we specified in our previous function
		localStorage.setItem('device', JSON.stringify(adsDeviceRecord)); // set the local storage item with the name and value, with the desired expiration date
	}

	var device = adsDeviceRecord || JSON.parse(localStorage.getItem('device')); // the value we found or was previously set
	var isAdsDeviceValid = device && new Date().getTime() < device.expiryDate; // variable if param value existed and had a date set previously

	// if we found the form input to add to, and there was a valid param value to send
	if (currAdsDeviceFormField && isAdsDeviceValid) {
		currAdsDeviceFormField.value = device.value; // set the form input value
	}
}
window.addEventListener('load', addAdsDevice);

I inspect the form on the site, and find the hidden input, and grab its id value. It's typically the form's ID, followed by an underscore, followed by the input's ID. So if you are working on Gravity Form #1 and on input's ID of #19, then the input should be input_1_19.