fixes

- use the fancy new syntax for optional chaining in JoinButton.js
- media-query comment and simplification

modules/tribes/client/components/JoinButton.js

@@ -59,9 +59,7 @@ export default function JoinButton({ tribe, user, onUpdated, ...rest }) {
 
   const [isUpdating, setIsUpdating] = useState(false);
 
-  // This should always be true or false, even when user is null.
-  // Therefore we convert the output to boolean.
-  const isMemberInitial = Boolean(user && user.memberIds && user.memberIds.indexOf(tribe._id) > -1);
+  const isMemberInitial = (user?.memberIds || []).includes(tribe._id);
   const [isMember, setIsMember] = useState(isMemberInitial);
 
   /**

modules/tribes/client/components/TribesList.component.js

@@ -15,15 +15,16 @@ const Item = styled.li`
   display: inline-block;
   vertical-align: bottom;
 
-  @media (min-width: 0) {
-    width: 100%;
-  }
+  // on small screens there is just one column of tribes
+  width: 100%;
 
   @media (min-width: 616px) {
+    // two columns of tribes
     width: 50%;
   }
 
   @media (min-width: 992px) {
+    // three columns of tribes
     width: 33.3333%;
   }
 `;