diff --git a/js/src/common/components/Button.tsx b/js/src/common/components/Button.tsx
index 93138eb81..6f03242c4 100644
--- a/js/src/common/components/Button.tsx
+++ b/js/src/common/components/Button.tsx
@@ -53,7 +53,7 @@ export default class Button<T extends ButtonProps = ButtonProps> extends Compone
 
         const loading = extract(attrs, 'loading');
         if (attrs.disabled || loading) {
-            attrs.className += ' ' + classNames('disabled', loading && 'loading');
+            attrs.className = classNames(attrs.className, 'disabled', loading && 'loading');
             delete attrs.onclick;
         }
 
diff --git a/js/src/common/helpers/listItems.tsx b/js/src/common/helpers/listItems.tsx
index cd1ce2f31..ddd12ee97 100644
--- a/js/src/common/helpers/listItems.tsx
+++ b/js/src/common/helpers/listItems.tsx
@@ -43,7 +43,7 @@ export default function listItems(items) {
             item
         ) : (
             <li
-                className={classNames(className, [item.itemName && `item-${item.itemName}`, active && 'active'])}
+                className={classNames(className, item.itemName && `item-${item.itemName}`, active && 'active')}
                 key={item.attrs?.key || item.itemName}
             >
                 {item}
diff --git a/js/src/forum/components/CommentPost.tsx b/js/src/forum/components/CommentPost.tsx
index 3420ab440..a12a56b6b 100644
--- a/js/src/forum/components/CommentPost.tsx
+++ b/js/src/forum/components/CommentPost.tsx
@@ -81,16 +81,14 @@ export default class CommentPost extends Post {
         const post = this.props.post;
         const attrs = super.attrs();
 
-        attrs.className =
-            (attrs.className || '') +
-            ' ' +
-            classNames({
-                CommentPost: true,
-                'Post--hidden': post.isHidden(),
-                'Post--edited': post.isEdited(),
-                revealContent: this.revealContent,
-                editing: this.isEditing(),
-            });
+        attrs.className = classNames(
+            attrs.className,
+            'CommentPost',
+            post.isHidden() && 'Post--hidden',
+            post.isEdited() && 'Post--edited',
+            this.revealContent && 'revealContent',
+            this.isEditing() && 'editing'
+        );
 
         return attrs;
     }
diff --git a/js/src/forum/components/Search.tsx b/js/src/forum/components/Search.tsx
index cfafc57e9..1c438bccd 100644
--- a/js/src/forum/components/Search.tsx
+++ b/js/src/forum/components/Search.tsx
@@ -76,15 +76,13 @@ export default class Search extends Component {
 
         return (
             <div
-                className={
-                    'Search ' +
-                    classNames({
-                        open: this.value() && this.hasFocus,
-                        focused: this.hasFocus,
-                        active: !!currentSearch,
-                        loading: !!this.loadingSources,
-                    })
-                }
+                className={classNames(
+                    'Search',
+                    this.value() && this.hasFocus && 'open',
+                    this.hasFocus && 'focused',
+                    !!currentSearch && 'active',
+                    !!this.loadingSources && 'loading'
+                )}
             >
                 <div className="Search-input">
                     <input
@@ -143,7 +141,7 @@ export default class Search extends Component {
 
         // Handle input key events on the search input, triggering results to load.
         $input
-            .on('input focus', function() {
+            .on('input focus', function(this: HTMLInputElement) {
                 const query = this.value.toLowerCase();
 
                 if (!query) return;