Create background-main.js

ext/bg/background.html

@@ -24,6 +24,7 @@
 
         <script src="/bg/js/anki.js"></script>
         <script src="/bg/js/anki-note-builder.js"></script>
+        <script src="/bg/js/backend.js"></script>
         <script src="/bg/js/mecab.js"></script>
         <script src="/bg/js/audio-uri-builder.js"></script>
         <script src="/bg/js/backend-api-forwarder.js"></script>
@@ -45,6 +46,6 @@
         <script src="/bg/js/util.js"></script>
         <script src="/mixed/js/audio-system.js"></script>
 
-        <script src="/bg/js/backend.js"></script>
+        <script src="/bg/js/background-main.js"></script>
     </body>
 </html>

ext/bg/js/backend.js

@@ -1054,6 +1054,3 @@ class Backend {
         }
     }
 }
-
-window.yomichanBackend = new Backend();
-window.yomichanBackend.prepare();

ext/bg/js/background-main.js

@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2020  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* global
+ * Backend
+ */
+
+async function main() {
+    window.yomichanBackend = new Backend();
+    await window.yomichanBackend.prepare();
+}
+
+main();