diff --git a/adminer/include/design.inc.php b/adminer/include/design.inc.php
index 93c968f6..f2d691cc 100644
--- a/adminer/include/design.inc.php
+++ b/adminer/include/design.inc.php
@@ -82,7 +82,7 @@ fQIDAQAB
 	echo script("mixin(document.body, {onkeydown: bodyKeydown, onclick: bodyClick"
 		. (isset($_COOKIE["adminer_version"]) ? "" : ", onload: partial(verifyVersion, '$VERSION', '" . js_escape(ME) . "', '" . get_token() . "')") // $token may be empty in auth.inc.php
 		. "});
-document.body.className = document.body.className.replace(/ nojs/, ' js');
+document.body.classList.replace('nojs', 'js');
 const offlineMessage = '" . js_escape(lang('You are offline.')) . "';
 const thousandsSeparator = '" . js_escape(lang(',')) . "';")
 	;
diff --git a/adminer/static/editing.js b/adminer/static/editing.js
index ea1f13dc..6a517166 100644
--- a/adminer/static/editing.js
+++ b/adminer/static/editing.js
@@ -696,7 +696,7 @@ function schemaMousemove(event) {
 		const top = (event.clientY - y) / em;
 		const lineSet = { };
 		for (const div of qsa('div', that)) {
-			if (div.className == 'references') {
+			if (div.classList.contains('references')) {
 				const div2 = qs('[id="' + (/^refs/.test(div.id) ? 'refd' : 'refs') + div.id.substr(4) + '"]');
 				const ref = (tablePos[div.title] || [ div2.parentNode.offsetTop / em, 0 ]);
 				let left1 = -1;
diff --git a/adminer/static/functions.js b/adminer/static/functions.js
index 048d2608..3754da97 100644
--- a/adminer/static/functions.js
+++ b/adminer/static/functions.js
@@ -69,7 +69,7 @@ function mixin(target, source) {
 */
 function alterClass(el, className, enable) {
 	if (el) {
-		el.className = el.className.replace(RegExp('(^|\\s)' + className + '(\\s|$)'), '$2') + (enable ? ' ' + className : '');
+		el.classList[enable ? 'add' : 'remove'](className);
 	}
 }
 
@@ -79,7 +79,7 @@ function alterClass(el, className, enable) {
 */
 function toggle(id) {
 	const el = qs('#' + id);
-	alterClass(el, 'hidden', !/(^|\s)hidden(\s|$)/.test(el.className));
+	el && el.classList.toggle('hidden');
 	return false;
 }
 
diff --git a/editor/static/editing.js b/editor/static/editing.js
index b03d8164..c7dcdcfd 100644
--- a/editor/static/editing.js
+++ b/editor/static/editing.js
@@ -32,7 +32,7 @@ function whisper(url) {
 			const a = field.nextSibling.firstChild;
 			if (a && a.firstChild.data == field.value) {
 				field.previousSibling.value = decodeURIComponent(a.href.replace(/.*=/, ''));
-				a.className = 'active';
+				a.classList.add('active');
 			}
 		}
 	});
diff --git a/plugins/codemirror.php b/plugins/codemirror.php
index ed5fdb24..62c2472f 100644
--- a/plugins/codemirror.php
+++ b/plugins/codemirror.php
@@ -56,7 +56,7 @@ function getCmMode(el) {
 for (const el of qsa('code')) {
 	const mode = getCmMode(el);
 	if (mode) {
-		el.className += ' cm-s-default';
+		el.classList.add('cm-s-default');
 		CodeMirror.runMode(el.textContent, mode, el);
 	}
 }