Update background global object usage (#556)

* Omit global window object for scripts used on the background page

* Validate document exists before using

* Remove dom.js from background.html

1 files changed, 5 insertions, 2 deletions

diff --git a/ext/bg/js/background-main.js b/ext/bg/js/background-main.js
index 24117f4e..345b4a77 100644
--- a/ext/bg/js/background-main.js
+++ b/ext/bg/js/background-main.js
@@ -20,6 +20,9 @@
  */
 
 (async () => {
-    window.yomichanBackend = new Backend();
-    await window.yomichanBackend.prepare();
+    const backend = new Backend();
+    if (typeof window === 'object' && window !== null) {
+        window.yomichanBackend = backend;
+    }
+    await backend.prepare();
 })();