2 files changed, 46 insertions, 2 deletions
diff --git a/ext/js/dom/popup-menu.js b/ext/js/dom/popup-menu.js
index 78394c93..33cdd1ae 100644
--- a/ext/js/dom/popup-menu.js
+++ b/ext/js/dom/popup-menu.js
@@ -17,6 +17,7 @@
  */
 
 import {EventDispatcher, EventListenerCollection} from '../core.js';
+import {querySelectorNotNull} from './query-selector.js';
 
 /**
  * @augments EventDispatcher<import('popup-menu').EventType>
@@ -33,9 +34,9 @@ export class PopupMenu extends EventDispatcher {
         /** @type {HTMLElement} */
         this._containerNode = containerNode;
         /** @type {HTMLElement} */
-        this._node = /** @type {HTMLElement} */ (containerNode.querySelector('.popup-menu'));
+        this._node = querySelectorNotNull(containerNode, '.popup-menu');
         /** @type {HTMLElement} */
-        this._bodyNode = /** @type {HTMLElement} */ (containerNode.querySelector('.popup-menu-body'));
+        this._bodyNode = querySelectorNotNull(containerNode, '.popup-menu-body');
         /** @type {boolean} */
         this._isClosed = false;
         /** @type {EventListenerCollection} */
diff --git a/ext/js/dom/query-selector.js b/ext/js/dom/query-selector.js
new file mode 100644
index 00000000..e881211d
--- /dev/null
+++ b/ext/js/dom/query-selector.js
@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2023  Yomitan 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/>.
+ */
+
+import {ExtensionError} from '../core/extension-error.js';
+
+/**
+ * @param {Element|Document|DocumentFragment} element
+ * @param {string} selector
+ * @returns {ExtensionError}
+ */
+function createError(element, selector) {
+    const error = new ExtensionError(`Performing querySelectorNotNull(element, ${JSON.stringify(selector)}) returned null`);
+    error.data = {element, selector};
+    return error;
+}
+
+/**
+ * @template {Element} T
+ * @param {Element|Document|DocumentFragment} element
+ * @param {string} selector
+ * @returns {T}
+ * @throws {Error}
+ */
+export function querySelectorNotNull(element, selector) {
+    /** @type {?T} */
+    const result = element.querySelector(selector);
+    if (result === null) { throw createError(element, selector); }
+    return result;
+}