change this https://watchpeopledie.tv/h/meta/post/61549/megathread-for-bugs-and-suggestions/2681468#context

files/assets/js/contact.js

@@ -0,0 +1,7 @@
+function contact(form) {
+	sendFormXHR(form,
+		() => {
+			document.getElementById('input-message').value = null;
+		}
+	)
+}

files/templates/contact.html

@@ -3,7 +3,7 @@
 {% block content %}
 	<h1 class="article-title">Contact {{SITE_NAME}} Admins</h1>
 	{% if v %}
-		<form id="contactform" action="/contact" method="post" enctype="multipart/form-data" data-nonce="{{g.nonce}}" data-onsubmit="sendFormXHR(this)">
+		<form id="contactform" action="/contact" method="post" enctype="multipart/form-data" data-nonce="{{g.nonce}}" data-onsubmit="contact(this)">
 			<label for="input-message" class="mt-3">Your message</label>
 			<input hidden name="formkey" value="{{v|formkey}}">
 			<textarea autocomplete="off" maxlength="10000" id="input-message" form="contactform" name="message" class="file-ta form-control" required></textarea>
@@ -24,4 +24,6 @@
 	{% else %}
 		<h4>by email: {{EMAIL}}</h4>
 	{% endif %}
+
+	<script defer src="{{'js/contact.js' | asset}}"></script>
 {% endblock %}