resolve reCaptcha on submit to prevent timeout

Documentation warns against resolving reCaptcha on page load:
https://developers.google.com/recaptcha/docs/v3
> Note: reCAPTCHA tokens expire after two minutes. If you're protecting an action with reCAPTCHA, make sure to call execute when the user takes the action rather than on page load.

My modification does just that.

assets/invisibleRecaptcha.js

@@ -1,26 +1,74 @@
 (function(document, Nette, grecaptcha) {
 	var init = false;
+
+	// polyfill for closest() - method for traversing DOM and finding the closest parent matching given selector (form, in our case)
+	// @see https://developer.mozilla.org/en-US/docs/Web/API/Element/closest#Polyfill
+	if (!Element.prototype.matches) {
+		Element.prototype.matches =
+			Element.prototype.msMatchesSelector ||
+			Element.prototype.mozMatchesSelector ||
+			Element.prototype.webkitMatchesSelector;
+	}
+
+	if (!Element.prototype.closest) {
+		Element.prototype.closest = function(s) {
+			var el = this;
+
+			do {
+				if (Element.prototype.matches.call(el, s)) return el;
+				el = el.parentElement || el.parentNode;
+			} while (el !== null && el.nodeType === 1);
+			return null;
+		};
+	}
+
 	Nette.recaptcha = function (grecaptcha) {
 		var items = document.getElementsByClassName('g-recaptcha');
 		var length = items.length;
 
-		if (length > 0) {
-			grecaptcha.ready(function () {
-				for (var i = 0; i < length; i++) {
-					grecaptcha.render(items[i]);
-				};
-				grecaptcha.execute().then(function (token) {
-					var inputs = document.getElementsByClassName('g-recaptcha-response');
-					for (var i = 0; i < items.length; i++) {
-						inputs[i].value = token;
-					};
-				});
-			});
-			init = true;
+		if (length === 0) {
+			return;
 		}
+
+		grecaptcha.ready(function () {
+			var resolved = false;
+			var submitListenerFactory = function(form) {
+				return function (e) {
+					// we already have reCaptcha response, or the form is invalid - or submission is prevented for some other, unknown reason
+					if (resolved || e.defaultPrevented) {
+						return;
+					}
+
+					e.preventDefault();
+
+					grecaptcha.execute().then(function (token) {
+						resolved = true;
+
+						// reCaptcha token expires after 2 minutes; make it 5 seconds earlier just in case network is slow
+						setTimeout(function(){ resolved = false; }, (2 * 60 - 5) * 1000);
+
+						var inputs = document.getElementsByClassName('g-recaptcha-response');
+						for (var i = 0; i < inputs.length; i++) {
+							inputs[i].value = token;
+						}
+
+						form.submit();
+					});
+				};
+			};
+
+			var form;
+			for (var i = 0; i < length; i++) {
+				grecaptcha.render(items[i]);
+
+				form = items[i].closest('form');
+				form.addEventListener('submit', submitListenerFactory(form));
+			}
+		});
+		init = true;
 	};
 
 	if (!init) {
 		Nette.recaptcha(grecaptcha);
 	}
-})(document, Nette, grecaptcha);
+})(document, Nette, grecaptcha);