5 files changed, 18 insertions, 16 deletions
diff --git a/ext/bg/background.html b/ext/bg/background.html
index ca35a3c6..53e8b140 100644
--- a/ext/bg/background.html
+++ b/ext/bg/background.html
@@ -20,7 +20,6 @@
         <script src="/mixed/lib/wanakana.min.js"></script>
 
         <script src="/mixed/js/core.js"></script>
-        <script src="/mixed/js/dom.js"></script>
         <script src="/mixed/js/environment.js"></script>
         <script src="/mixed/js/japanese.js"></script>
 
diff --git a/ext/bg/js/anki-note-builder.js b/ext/bg/js/anki-note-builder.js
index 76199db7..31e67394 100644
--- a/ext/bg/js/anki-note-builder.js
+++ b/ext/bg/js/anki-note-builder.js
@@ -155,7 +155,7 @@ class AnkiNoteBuilder {
     }
 
     static arrayBufferToBase64(arrayBuffer) {
-        return window.btoa(String.fromCharCode(...new Uint8Array(arrayBuffer)));
+        return btoa(String.fromCharCode(...new Uint8Array(arrayBuffer)));
     }
 
     static stringReplaceAsync(str, regex, replacer) {
diff --git a/ext/bg/js/backend.js b/ext/bg/js/backend.js
index 90895737..80b00d5f 100644
--- a/ext/bg/js/backend.js
+++ b/ext/bg/js/backend.js
@@ -65,12 +65,14 @@ class Backend {
             renderTemplate: this._renderTemplate.bind(this)
         });
 
-        this.optionsContext = {
-            depth: 0,
-            url: window.location.href
-        };
+        const url = (typeof window === 'object' && window !== null ? window.location.href : '');
+        this.optionsContext = {depth: 0, url};
 
-        this.clipboardPasteTarget = document.querySelector('#clipboard-paste-target');
+        this.clipboardPasteTarget = (
+            typeof document === 'object' && document !== null ?
+            document.querySelector('#clipboard-paste-target') :
+            null
+        );
 
         this.popupWindow = null;
 
@@ -704,6 +706,9 @@ class Backend {
             return await navigator.clipboard.readText();
         } else {
             const clipboardPasteTarget = this.clipboardPasteTarget;
+            if (clipboardPasteTarget === null) {
+                throw new Error('Reading the clipboard is not supported in this context');
+            }
             clipboardPasteTarget.value = '';
             clipboardPasteTarget.focus();
             document.execCommand('paste');
@@ -1005,13 +1010,8 @@ class Backend {
     }
 
     async _onCommandToggle() {
-        const optionsContext = {
-            depth: 0,
-            url: window.location.href
-        };
         const source = 'popup';
-
-        const options = this.getOptions(optionsContext);
+        const options = this.getOptions(this.optionsContext);
         options.general.enable = !options.general.enable;
         await this._onApiOptionsSave({source});
     }
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();
 })();
diff --git a/ext/bg/js/database.js b/ext/bg/js/database.js
index 930cd0d0..65e267ab 100644
--- a/ext/bg/js/database.js
+++ b/ext/bg/js/database.js
@@ -596,7 +596,7 @@ class Database {
 
     static _open(name, version, onUpgradeNeeded) {
         return new Promise((resolve, reject) => {
-            const request = window.indexedDB.open(name, version * 10);
+            const request = indexedDB.open(name, version * 10);
 
             request.onupgradeneeded = (event) => {
                 try {