Suppress CORS errors in the 'failed to join room' dialog

src/i18n/strings/en_EN.json

@@ -221,6 +221,7 @@
     "Your browser does not support the required cryptography extensions": "Your browser does not support the required cryptography extensions",
     "Not a valid Riot keyfile": "Not a valid Riot keyfile",
     "Authentication check failed: incorrect password?": "Authentication check failed: incorrect password?",
+    "There was an error joining the room": "There was an error joining the room",
     "Use a few words, avoid common phrases": "Use a few words, avoid common phrases",
     "No need for symbols, digits, or uppercase letters": "No need for symbols, digits, or uppercase letters",
     "Use a longer keyboard pattern with more turns": "Use a longer keyboard pattern with more turns",

src/stores/RoomViewStore.js

@@ -224,6 +224,11 @@ class RoomViewStore extends Store {
                 err: err,
             });
             let msg = err.message ? err.message : JSON.stringify(err);
+            // XXX: We are relying on the error message returned by browsers here.
+            // This isn't great, but it does generalize the error being shown to users.
+            if (msg && msg.startsWith("CORS request rejected")) {
+                msg = _t("There was an error joining the room");
+            }
             if (err.errcode === 'M_INCOMPATIBLE_ROOM_VERSION') {
                 msg = <div>
                     {_t("Sorry, your homeserver is too old to participate in this room.")}<br />