Add JSDoc type annotations to project (rebased)

7 files changed, 742 insertions, 280 deletions

diff --git a/ext/js/app/content-script-main.js b/ext/js/app/content-script-main.js
index a042f3bf..972d032c 100644
--- a/ext/js/app/content-script-main.js
+++ b/ext/js/app/content-script-main.js
@@ -46,7 +46,9 @@ import {PopupFactory} from './popup-factory.js';
             parentFrameId: null,
             useProxyPopup: false,
             pageType: 'web',
+            canUseWindowPopup: true,
             allowRootFramePopupProxy: true,
+            childrenSupported: true,
             hotkeyHandler
         });
         await frontend.prepare();
diff --git a/ext/js/app/frontend.js b/ext/js/app/frontend.js
index 4c13eac2..fec933f8 100644
--- a/ext/js/app/frontend.js
+++ b/ext/js/app/frontend.js
@@ -17,7 +17,7 @@
  */
 
 import {GoogleDocsUtil} from '../accessibility/google-docs-util.js';
-import {EventListenerCollection, invokeMessageHandler, isObject, log, promiseAnimationFrame} from '../core.js';
+import {EventListenerCollection, invokeMessageHandler, log, promiseAnimationFrame} from '../core.js';
 import {DocumentUtil} from '../dom/document-util.js';
 import {TextSourceElement} from '../dom/text-source-element.js';
 import {TextSourceRange} from '../dom/text-source-range.js';
@@ -25,7 +25,6 @@ import {HotkeyHandler} from '../input/hotkey-handler.js';
 import {TextScanner} from '../language/text-scanner.js';
 import {yomitan} from '../yomitan.js';
 import {PopupFactory} from './popup-factory.js';
-import {Popup} from './popup.js';
 
 /**
  * This is the main class responsible for scanning and handling webpage content.
@@ -33,19 +32,7 @@ import {Popup} from './popup.js';
 export class Frontend {
     /**
      * Creates a new instance.
-     * @param {object} details Details about how to set up the instance.
-     * @param {string} details.pageType The type of page, one of 'web', 'popup', or 'search'.
-     * @param {PopupFactory} details.popupFactory A PopupFactory instance to use for generating popups.
-     * @param {number} details.depth The nesting depth value of the popup.
-     * @param {number} details.tabId The tab ID of the host tab.
-     * @param {number} details.frameId The frame ID of the host frame.
-     * @param {?string} details.parentPopupId The popup ID of the parent popup if one exists, otherwise null.
-     * @param {?number} details.parentFrameId The frame ID of the parent popup if one exists, otherwise null.
-     * @param {boolean} details.useProxyPopup Whether or not proxy popups should be used.
-     * @param {boolean} details.canUseWindowPopup Whether or not window popups can be used.
-     * @param {boolean} details.allowRootFramePopupProxy Whether or not popups can be hosted in the root frame.
-     * @param {boolean} details.childrenSupported Whether popups can create child popups or not.
-     * @param {HotkeyHandler} details.hotkeyHandler A HotkeyHandler instance.
+     * @param {import('frontend').ConstructorDetails} details Details about how to set up the instance.
      */
     constructor({
         pageType,
@@ -61,24 +48,43 @@ export class Frontend {
         childrenSupported=true,
         hotkeyHandler
     }) {
+        /** @type {import('frontend').PageType} */
         this._pageType = pageType;
+        /** @type {PopupFactory} */
         this._popupFactory = popupFactory;
+        /** @type {number} */
         this._depth = depth;
+        /** @type {number|undefined} */
         this._tabId = tabId;
+        /** @type {number} */
         this._frameId = frameId;
+        /** @type {?string} */
         this._parentPopupId = parentPopupId;
+        /** @type {?number} */
         this._parentFrameId = parentFrameId;
+        /** @type {boolean} */
         this._useProxyPopup = useProxyPopup;
+        /** @type {boolean} */
         this._canUseWindowPopup = canUseWindowPopup;
+        /** @type {boolean} */
         this._allowRootFramePopupProxy = allowRootFramePopupProxy;
+        /** @type {boolean} */
         this._childrenSupported = childrenSupported;
+        /** @type {HotkeyHandler} */
         this._hotkeyHandler = hotkeyHandler;
+        /** @type {?import('popup').PopupAny} */
         this._popup = null;
+        /** @type {boolean} */
         this._disabledOverride = false;
+        /** @type {?import('settings').ProfileOptions} */
         this._options = null;
+        /** @type {number} */
         this._pageZoomFactor = 1.0;
+        /** @type {number} */
         this._contentScale = 1.0;
+        /** @type {Promise<void>} */
         this._lastShowPromise = Promise.resolve();
+        /** @type {TextScanner} */
         this._textScanner = new TextScanner({
             node: window,
             ignoreElements: this._ignoreElements.bind(this),
@@ -87,19 +93,27 @@ export class Frontend {
             searchTerms: true,
             searchKanji: true
         });
+        /** @type {boolean} */
         this._textScannerHasBeenEnabled = false;
+        /** @type {Map<'default'|'window'|'iframe'|'proxy', Promise<?import('popup').PopupAny>>} */
         this._popupCache = new Map();
+        /** @type {EventListenerCollection} */
         this._popupEventListeners = new EventListenerCollection();
+        /** @type {?import('core').TokenObject} */
         this._updatePopupToken = null;
+        /** @type {?number} */
         this._clearSelectionTimer = null;
+        /** @type {boolean} */
         this._isPointerOverPopup = false;
+        /** @type {?import('settings').OptionsContext} */
         this._optionsContextOverride = null;
 
-        this._runtimeMessageHandlers = new Map([
+        /** @type {import('core').MessageHandlerMap} */
+        this._runtimeMessageHandlers = new Map(/** @type {import('core').MessageHandlerArray} */ ([
             ['Frontend.requestReadyBroadcast',   {async: false, handler: this._onMessageRequestFrontendReadyBroadcast.bind(this)}],
             ['Frontend.setAllVisibleOverride',   {async: true,  handler: this._onApiSetAllVisibleOverride.bind(this)}],
             ['Frontend.clearAllVisibleOverride', {async: true,  handler: this._onApiClearAllVisibleOverride.bind(this)}]
-        ]);
+        ]));
 
         this._hotkeyHandler.registerActions([
             ['scanSelectedText', this._onActionScanSelectedText.bind(this)],
@@ -125,7 +139,7 @@ export class Frontend {
 
     /**
      * Gets the popup instance.
-     * @type {Popup}
+     * @type {?import('popup').PopupAny}
      */
     get popup() {
         return this._popup;
@@ -148,8 +162,8 @@ export class Frontend {
         window.addEventListener('resize', this._onResize.bind(this), false);
         DocumentUtil.addFullscreenChangeEventListener(this._updatePopup.bind(this));
 
-        const visualViewport = window.visualViewport;
-        if (visualViewport !== null && typeof visualViewport === 'object') {
+        const {visualViewport} = window;
+        if (typeof visualViewport !== 'undefined' && visualViewport !== null) {
             visualViewport.addEventListener('scroll', this._onVisualViewportScroll.bind(this));
             visualViewport.addEventListener('resize', this._onVisualViewportResize.bind(this));
         }
@@ -172,7 +186,7 @@ export class Frontend {
 
         this._prepareSiteSpecific();
         this._updateContentScale();
-        this._signalFrontendReady();
+        this._signalFrontendReady(null);
     }
 
     /**
@@ -186,7 +200,7 @@ export class Frontend {
 
     /**
      * Set or clear an override options context object.
-     * @param {?object} optionsContext An options context object to use as the override, or `null` to clear the override.
+     * @param {?import('settings').OptionsContext} optionsContext An options context object to use as the override, or `null` to clear the override.
      */
     setOptionsContextOverride(optionsContext) {
         this._optionsContextOverride = optionsContext;
@@ -194,7 +208,7 @@ export class Frontend {
 
     /**
      * Performs a new search on a specific source.
-     * @param {TextSourceRange|TextSourceElement} textSource The text source to search.
+     * @param {import('text-source').TextSource} textSource The text source to search.
      */
     async setTextSource(textSource) {
         this._textScanner.setCurrentTextSource(null);
@@ -216,7 +230,7 @@ export class Frontend {
 
     /**
      * Waits for the previous `showContent` call to be completed.
-     * @returns {Promise} A promise which is resolved when the previous `showContent` call has completed.
+     * @returns {Promise<void>} A promise which is resolved when the previous `showContent` call has completed.
      */
     showContentCompleted() {
         return this._lastShowPromise;
@@ -224,45 +238,73 @@ export class Frontend {
 
     // Message handlers
 
+    /**
+     * @param {import('frontend').FrontendRequestReadyBroadcastParams} params
+     */
     _onMessageRequestFrontendReadyBroadcast({frameId}) {
         this._signalFrontendReady(frameId);
     }
 
     // Action handlers
 
+    /**
+     * @returns {void}
+     */
     _onActionScanSelectedText() {
         this._scanSelectedText(false);
     }
 
+    /**
+     * @returns {void}
+     */
     _onActionScanTextAtCaret() {
         this._scanSelectedText(true);
     }
 
     // API message handlers
 
+    /**
+     * @returns {string}
+     */
     _onApiGetUrl() {
         return window.location.href;
     }
 
+    /**
+     * @returns {void}
+     */
     _onApiClosePopup() {
         this._clearSelection(false);
     }
 
+    /**
+     * @returns {void}
+     */
     _onApiCopySelection() {
         // This will not work on Firefox if a popup has focus, which is usually the case when this function is called.
         document.execCommand('copy');
     }
 
+    /**
+     * @returns {string}
+     */
     _onApiGetSelectionText() {
-        return document.getSelection().toString();
+        const selection = document.getSelection();
+        return selection !== null ? selection.toString() : '';
     }
 
+    /**
+     * @returns {import('frontend').GetPopupInfoResult}
+     */
     _onApiGetPopupInfo() {
         return {
             popupId: (this._popup !== null ? this._popup.id : null)
         };
     }
 
+    /**
+     * @returns {{url: string, documentTitle: string}}
+     */
     _onApiGetPageInfo() {
         return {
             url: window.location.href,
@@ -270,6 +312,10 @@ export class Frontend {
         };
     }
 
+    /**
+     * @param {{value: boolean, priority: number, awaitFrame: boolean}} params
+     * @returns {Promise<import('core').TokenString>}
+     */
     async _onApiSetAllVisibleOverride({value, priority, awaitFrame}) {
         const result = await this._popupFactory.setAllVisibleOverride(value, priority);
         if (awaitFrame) {
@@ -278,45 +324,71 @@ export class Frontend {
         return result;
     }
 
+    /**
+     * @param {{token: import('core').TokenString}} params
+     * @returns {Promise<boolean>}
+     */
     async _onApiClearAllVisibleOverride({token}) {
         return await this._popupFactory.clearAllVisibleOverride(token);
     }
 
     // Private
 
+    /**
+     * @returns {void}
+     */
     _onResize() {
         this._updatePopupPosition();
     }
 
+    /** @type {import('extension').ChromeRuntimeOnMessageCallback} */
     _onRuntimeMessage({action, params}, sender, callback) {
         const messageHandler = this._runtimeMessageHandlers.get(action);
         if (typeof messageHandler === 'undefined') { return false; }
         return invokeMessageHandler(messageHandler, params, callback, sender);
     }
 
+    /**
+     * @param {{newZoomFactor: number}} params
+     */
     _onZoomChanged({newZoomFactor}) {
         this._pageZoomFactor = newZoomFactor;
         this._updateContentScale();
     }
 
+    /**
+     * @returns {void}
+     */
     _onClosePopups() {
         this._clearSelection(true);
     }
 
+    /**
+     * @returns {void}
+     */
     _onVisualViewportScroll() {
         this._updatePopupPosition();
     }
 
+    /**
+     * @returns {void}
+     */
     _onVisualViewportResize() {
         this._updateContentScale();
     }
 
+    /**
+     * @returns {void}
+     */
     _onTextScannerClear() {
         this._clearSelection(false);
     }
 
-    _onSearched({type, dictionaryEntries, sentence, inputInfo: {eventType, passive, detail}, textSource, optionsContext, detail: {documentTitle}, error}) {
-        const scanningOptions = this._options.scanning;
+    /**
+     * @param {import('text-scanner').SearchedEventDetails} details
+     */
+    _onSearched({type, dictionaryEntries, sentence, inputInfo: {eventType, passive, detail: inputInfoDetail}, textSource, optionsContext, detail, error}) {
+        const scanningOptions = /** @type {import('settings').ProfileOptions} */ (this._options).scanning;
 
         if (error !== null) {
             if (yomitan.isExtensionUnloaded) {
@@ -326,34 +398,43 @@ export class Frontend {
             } else {
                 log.error(error);
             }
-        } if (type !== null) {
+        } if (type !== null && optionsContext !== null) {
             this._stopClearSelectionDelayed();
             let focus = (eventType === 'mouseMove');
-            if (isObject(detail)) {
-                const focus2 = detail.focus;
+            if (typeof inputInfoDetail === 'object' && inputInfoDetail !== null) {
+                const focus2 = inputInfoDetail.focus;
                 if (typeof focus2 === 'boolean') { focus = focus2; }
             }
-            this._showContent(textSource, focus, dictionaryEntries, type, sentence, documentTitle, optionsContext);
+            this._showContent(textSource, focus, dictionaryEntries, type, sentence, detail !== null ? detail.documentTitle : null, optionsContext);
         } else {
             if (scanningOptions.autoHideResults) {
-                this._clearSelectionDelayed(scanningOptions.hideDelay, false);
+                this._clearSelectionDelayed(scanningOptions.hideDelay, false, false);
             }
         }
     }
 
+    /**
+     * @returns {void}
+     */
     _onPopupFramePointerOver() {
         this._isPointerOverPopup = true;
         this._stopClearSelectionDelayed();
     }
 
+    /**
+     * @returns {void}
+     */
     _onPopupFramePointerOut() {
         this._isPointerOverPopup = false;
-        const scanningOptions = this._options.scanning;
+        const scanningOptions = /** @type {import('settings').ProfileOptions} */ (this._options).scanning;
         if (scanningOptions.hidePopupOnCursorExit) {
-            this._clearSelectionDelayed(scanningOptions.hidePopupOnCursorExitDelay, false);
+            this._clearSelectionDelayed(scanningOptions.hidePopupOnCursorExitDelay, false, false);
         }
     }
 
+    /**
+     * @param {boolean} passive
+     */
     _clearSelection(passive) {
         this._stopClearSelectionDelayed();
         if (this._popup !== null) {
@@ -364,6 +445,11 @@ export class Frontend {
         this._textScanner.clearSelection();
     }
 
+    /**
+     * @param {number} delay
+     * @param {boolean} restart
+     * @param {boolean} passive
+     */
     _clearSelectionDelayed(delay, restart, passive) {
         if (!this._textScanner.hasSelection()) { return; }
         if (delay > 0) {
@@ -379,6 +465,9 @@ export class Frontend {
         }
     }
 
+    /**
+     * @returns {void}
+     */
     _stopClearSelectionDelayed() {
         if (this._clearSelectionTimer !== null) {
             clearTimeout(this._clearSelectionTimer);
@@ -386,6 +475,9 @@ export class Frontend {
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _updateOptionsInternal() {
         const optionsContext = await this._getOptionsContext();
         const options = await yomitan.api.optionsGet(optionsContext);
@@ -426,12 +518,16 @@ export class Frontend {
         await this._textScanner.searchLast();
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _updatePopup() {
-        const {usePopupWindow, showIframePopupsInRootFrame} = this._options.general;
+        const {usePopupWindow, showIframePopupsInRootFrame} = /** @type {import('settings').ProfileOptions} */ (this._options).general;
         const isIframe = !this._useProxyPopup && (window !== window.parent);
 
         const currentPopup = this._popup;
 
+        /** @type {Promise<?import('popup').PopupAny>|undefined} */
         let popupPromise;
         if (usePopupWindow && this._canUseWindowPopup) {
             popupPromise = this._popupCache.get('window');
@@ -466,6 +562,7 @@ export class Frontend {
 
         // The token below is used as a unique identifier to ensure that a new _updatePopup call
         // hasn't been started during the await.
+        /** @type {?import('core').TokenObject} */
         const token = {};
         this._updatePopupToken = token;
         const popup = await popupPromise;
@@ -489,6 +586,9 @@ export class Frontend {
         this._isPointerOverPopup = false;
     }
 
+    /**
+     * @returns {Promise<?import('popup').PopupAny>}
+     */
     async _getDefaultPopup() {
         const isXmlDocument = (typeof XMLDocument !== 'undefined' && document instanceof XMLDocument);
         if (isXmlDocument) {
@@ -502,6 +602,9 @@ export class Frontend {
         });
     }
 
+    /**
+     * @returns {Promise<import('popup').PopupAny>}
+     */
     async _getProxyPopup() {
         return await this._popupFactory.getOrCreatePopup({
             frameId: this._parentFrameId,
@@ -511,6 +614,9 @@ export class Frontend {
         });
     }
 
+    /**
+     * @returns {Promise<?import('popup').PopupAny>}
+     */
     async _getIframeProxyPopup() {
         const targetFrameId = 0; // Root frameId
         try {
@@ -520,7 +626,8 @@ export class Frontend {
             return await this._getDefaultPopup();
         }
 
-        const {popupId} = await yomitan.crossFrame.invoke(targetFrameId, 'Frontend.getPopupInfo');
+        /** @type {import('frontend').GetPopupInfoResult} */
+        const {popupId} = await yomitan.crossFrame.invoke(targetFrameId, 'Frontend.getPopupInfo', {});
         if (popupId === null) {
             return null;
         }
@@ -537,6 +644,9 @@ export class Frontend {
         return popup;
     }
 
+    /**
+     * @returns {Promise<import('popup').PopupAny>}
+     */
     async _getPopupWindow() {
         return await this._popupFactory.getOrCreatePopup({
             depth: this._depth,
@@ -545,6 +655,9 @@ export class Frontend {
         });
     }
 
+    /**
+     * @returns {Element[]}
+     */
     _ignoreElements() {
         if (this._popup !== null) {
             const container = this._popup.container;
@@ -555,6 +668,11 @@ export class Frontend {
         return [];
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @returns {Promise<boolean>}
+     */
     async _ignorePoint(x, y) {
         try {
             return this._popup !== null && await this._popup.containsPoint(x, y);
@@ -566,17 +684,44 @@ export class Frontend {
         }
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     */
     _showExtensionUnloaded(textSource) {
-        if (textSource === null) {
-            textSource = this._textScanner.getCurrentTextSource();
-            if (textSource === null) { return; }
-        }
         this._showPopupContent(textSource, null, null);
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     * @param {boolean} focus
+     * @param {?import('dictionary').DictionaryEntry[]} dictionaryEntries
+     * @param {import('display').PageType} type
+     * @param {?import('display').HistoryStateSentence} sentence
+     * @param {?string} documentTitle
+     * @param {import('settings').OptionsContext} optionsContext
+     */
     _showContent(textSource, focus, dictionaryEntries, type, sentence, documentTitle, optionsContext) {
         const query = textSource.text();
         const {url} = optionsContext;
+        /** @type {import('display').HistoryState} */
+        const detailsState = {
+            focusEntry: 0,
+            optionsContext,
+            url
+        };
+        if (sentence !== null) { detailsState.sentence = sentence; }
+        if (documentTitle !== null) { detailsState.documentTitle = documentTitle; }
+        /** @type {import('display').HistoryContent} */
+        const detailsContent = {
+            contentOrigin: {
+                tabId: this._tabId,
+                frameId: this._frameId
+            }
+        };
+        if (dictionaryEntries !== null) {
+            detailsContent.dictionaryEntries = dictionaryEntries;
+        }
+        /** @type {import('display').ContentDetails} */
         const details = {
             focus,
             historyMode: 'clear',
@@ -585,28 +730,22 @@ export class Frontend {
                 query,
                 wildcards: 'off'
             },
-            state: {
-                focusEntry: 0,
-                optionsContext,
-                url,
-                sentence,
-                documentTitle
-            },
-            content: {
-                dictionaryEntries,
-                contentOrigin: {
-                    tabId: this._tabId,
-                    frameId: this._frameId
-                }
-            }
+            state: detailsState,
+            content: detailsContent
         };
-        if (textSource.type === 'element' && textSource.fullContent !== query) {
+        if (textSource instanceof TextSourceElement && textSource.fullContent !== query) {
             details.params.full = textSource.fullContent;
             details.params['full-visible'] = 'true';
         }
         this._showPopupContent(textSource, optionsContext, details);
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     * @param {?import('settings').OptionsContext} optionsContext
+     * @param {?import('display').ContentDetails} details
+     * @returns {Promise<void>}
+     */
     _showPopupContent(textSource, optionsContext, details) {
         const sourceRects = [];
         for (const {left, top, right, bottom} of textSource.getRects()) {
@@ -631,6 +770,9 @@ export class Frontend {
         return this._lastShowPromise;
     }
 
+    /**
+     * @returns {void}
+     */
     _updateTextScannerEnabled() {
         const enabled = (this._options !== null && this._options.general.enable && !this._disabledOverride);
         if (enabled === this._textScanner.isEnabled()) { return; }
@@ -643,15 +785,18 @@ export class Frontend {
         }
     }
 
+    /**
+     * @returns {void}
+     */
     _updateContentScale() {
-        const {popupScalingFactor, popupScaleRelativeToPageZoom, popupScaleRelativeToVisualViewport} = this._options.general;
+        const {popupScalingFactor, popupScaleRelativeToPageZoom, popupScaleRelativeToVisualViewport} = /** @type {import('settings').ProfileOptions} */ (this._options).general;
         let contentScale = popupScalingFactor;
         if (popupScaleRelativeToPageZoom) {
             contentScale /= this._pageZoomFactor;
         }
         if (popupScaleRelativeToVisualViewport) {
-            const visualViewport = window.visualViewport;
-            const visualViewportScale = (visualViewport !== null && typeof visualViewport === 'object' ? visualViewport.scale : 1.0);
+            const {visualViewport} = window;
+            const visualViewportScale = (typeof visualViewport !== 'undefined' && visualViewport !== null ? visualViewport.scale : 1.0);
             contentScale /= visualViewportScale;
         }
         if (contentScale === this._contentScale) { return; }
@@ -663,6 +808,9 @@ export class Frontend {
         this._updatePopupPosition();
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _updatePopupPosition() {
         const textSource = this._textScanner.getCurrentTextSource();
         if (
@@ -674,7 +822,11 @@ export class Frontend {
         }
     }
 
-    _signalFrontendReady(targetFrameId=null) {
+    /**
+     * @param {?number} targetFrameId
+     */
+    _signalFrontendReady(targetFrameId) {
+        /** @type {import('frontend').FrontendReadyDetails} */
         const params = {frameId: this._frameId};
         if (targetFrameId === null) {
             yomitan.api.broadcastTab('frontendReady', params);
@@ -683,8 +835,14 @@ export class Frontend {
         }
     }
 
+    /**
+     * @param {number} frameId
+     * @param {?number} timeout
+     * @returns {Promise<void>}
+     */
     async _waitForFrontendReady(frameId, timeout) {
         return new Promise((resolve, reject) => {
+            /** @type {?number} */
             let timeoutId = null;
 
             const cleanup = () => {
@@ -694,10 +852,11 @@ export class Frontend {
                 }
                 chrome.runtime.onMessage.removeListener(onMessage);
             };
-            const onMessage = (message, sender, sendResponse) => {
+            /** @type {import('extension').ChromeRuntimeOnMessageCallback} */
+            const onMessage = (message, _sender, sendResponse) => {
                 try {
                     const {action, params} = message;
-                    if (action === 'frontendReady' && params.frameId === frameId) {
+                    if (action === 'frontendReady' && /** @type {import('frontend').FrontendReadyDetails} */ (params).frameId === frameId) {
                         cleanup();
                         resolve();
                         sendResponse();
@@ -720,6 +879,10 @@ export class Frontend {
         });
     }
 
+    /**
+     * @param {import('settings').PreventMiddleMouseOptions} preventMiddleMouseOptions
+     * @returns {boolean}
+     */
     _getPreventMiddleMouseValueForPageType(preventMiddleMouseOptions) {
         switch (this._pageType) {
             case 'web': return preventMiddleMouseOptions.onWebPages;
@@ -729,6 +892,9 @@ export class Frontend {
         }
     }
 
+    /**
+     * @returns {Promise<import('settings').OptionsContext>}
+     */
     async _getOptionsContext() {
         let optionsContext = this._optionsContextOverride;
         if (optionsContext === null) {
@@ -737,10 +903,13 @@ export class Frontend {
         return optionsContext;
     }
 
+    /**
+     * @returns {Promise<{optionsContext: import('settings').OptionsContext, detail?: import('text-scanner').SearchResultDetail}>}
+     */
     async _getSearchContext() {
         let url = window.location.href;
         let documentTitle = document.title;
-        if (this._useProxyPopup) {
+        if (this._useProxyPopup && this._parentFrameId !== null) {
             try {
                 ({url, documentTitle} = await yomitan.crossFrame.invoke(this._parentFrameId, 'Frontend.getPageInfo', {}));
             } catch (e) {
@@ -759,6 +928,10 @@ export class Frontend {
         };
     }
 
+    /**
+     * @param {boolean} allowEmptyRange
+     * @returns {Promise<boolean>}
+     */
     async _scanSelectedText(allowEmptyRange) {
         const range = this._getFirstSelectionRange(allowEmptyRange);
         if (range === null) { return false; }
@@ -767,8 +940,13 @@ export class Frontend {
         return true;
     }
 
+    /**
+     * @param {boolean} allowEmptyRange
+     * @returns {?Range}
+     */
     _getFirstSelectionRange(allowEmptyRange) {
         const selection = window.getSelection();
+        if (selection === null) { return null; }
         for (let i = 0, ii = selection.rangeCount; i < ii; ++i) {
             const range = selection.getRangeAt(i);
             if (range.toString().length > 0 || allowEmptyRange) {
@@ -778,6 +956,9 @@ export class Frontend {
         return null;
     }
 
+    /**
+     * @returns {void}
+     */
     _prepareSiteSpecific() {
         switch (location.hostname.toLowerCase()) {
             case 'docs.google.com':
@@ -786,6 +967,9 @@ export class Frontend {
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _prepareGoogleDocs() {
         if (typeof GoogleDocsUtil !== 'undefined') { return; }
         await yomitan.api.loadExtensionScripts([
diff --git a/ext/js/app/popup-factory.js b/ext/js/app/popup-factory.js
index e871f7ec..6fa50796 100644
--- a/ext/js/app/popup-factory.js
+++ b/ext/js/app/popup-factory.js
@@ -32,9 +32,13 @@ export class PopupFactory {
      * @param {number} frameId The frame ID of the host frame.
      */
     constructor(frameId) {
+        /** @type {number} */
         this._frameId = frameId;
+        /** @type {FrameOffsetForwarder} */
         this._frameOffsetForwarder = new FrameOffsetForwarder(frameId);
+        /** @type {Map<string, import('popup').PopupAny>} */
         this._popups = new Map();
+        /** @type {Map<string, {popup: import('popup').PopupAny, token: string}[]>} */
         this._allPopupVisibilityTokenMap = new Map();
     }
 
@@ -46,17 +50,17 @@ export class PopupFactory {
         yomitan.crossFrame.registerHandlers([
             ['PopupFactory.getOrCreatePopup',     {async: true,  handler: this._onApiGetOrCreatePopup.bind(this)}],
             ['PopupFactory.setOptionsContext',    {async: true,  handler: this._onApiSetOptionsContext.bind(this)}],
-            ['PopupFactory.hide',                 {async: false, handler: this._onApiHide.bind(this)}],
+            ['PopupFactory.hide',                 {async: true,  handler: this._onApiHide.bind(this)}],
             ['PopupFactory.isVisible',            {async: true,  handler: this._onApiIsVisibleAsync.bind(this)}],
             ['PopupFactory.setVisibleOverride',   {async: true,  handler: this._onApiSetVisibleOverride.bind(this)}],
             ['PopupFactory.clearVisibleOverride', {async: true,  handler: this._onApiClearVisibleOverride.bind(this)}],
             ['PopupFactory.containsPoint',        {async: true,  handler: this._onApiContainsPoint.bind(this)}],
             ['PopupFactory.showContent',          {async: true,  handler: this._onApiShowContent.bind(this)}],
-            ['PopupFactory.setCustomCss',         {async: false, handler: this._onApiSetCustomCss.bind(this)}],
-            ['PopupFactory.clearAutoPlayTimer',   {async: false, handler: this._onApiClearAutoPlayTimer.bind(this)}],
-            ['PopupFactory.setContentScale',      {async: false, handler: this._onApiSetContentScale.bind(this)}],
-            ['PopupFactory.updateTheme',          {async: false, handler: this._onApiUpdateTheme.bind(this)}],
-            ['PopupFactory.setCustomOuterCss',    {async: false, handler: this._onApiSetCustomOuterCss.bind(this)}],
+            ['PopupFactory.setCustomCss',         {async: true,  handler: this._onApiSetCustomCss.bind(this)}],
+            ['PopupFactory.clearAutoPlayTimer',   {async: true,  handler: this._onApiClearAutoPlayTimer.bind(this)}],
+            ['PopupFactory.setContentScale',      {async: true,  handler: this._onApiSetContentScale.bind(this)}],
+            ['PopupFactory.updateTheme',          {async: true,  handler: this._onApiUpdateTheme.bind(this)}],
+            ['PopupFactory.setCustomOuterCss',    {async: true,  handler: this._onApiSetCustomOuterCss.bind(this)}],
             ['PopupFactory.getFrameSize',         {async: true,  handler: this._onApiGetFrameSize.bind(this)}],
             ['PopupFactory.setFrameSize',         {async: true,  handler: this._onApiSetFrameSize.bind(this)}]
         ]);
@@ -64,14 +68,8 @@ export class PopupFactory {
 
     /**
      * Gets or creates a popup based on a set of parameters
-     * @param {object} details Details about how to acquire the popup.
-     * @param {?number} [details.frameId] The ID of the frame that should host the popup.
-     * @param {?string} [details.id] A specific ID used to find an existing popup, or to assign to the new popup.
-     * @param {?string} [details.parentPopupId] The ID of the parent popup.
-     * @param {?number} [details.depth] A specific depth value to assign to the popup.
-     * @param {boolean} [details.popupWindow] Whether or not a separate popup window should be used, rather than an iframe.
-     * @param {boolean} [details.childrenSupported] Whether or not the popup is able to show child popups.
-     * @returns {Popup|PopupWindow|PopupProxy} The new or existing popup.
+     * @param {import('popup-factory').GetOrCreatePopupDetails} details Details about how to acquire the popup.
+     * @returns {Promise<import('popup').PopupAny>}
      */
     async getOrCreatePopup({
         frameId=null,
@@ -140,7 +138,7 @@ export class PopupFactory {
                 if (parent.child !== null) {
                     throw new Error('Parent popup already has a child');
                 }
-                popup.parent = parent;
+                popup.parent = /** @type {Popup} */ (parent);
                 parent.child = popup;
             }
             this._popups.set(id, popup);
@@ -151,16 +149,18 @@ export class PopupFactory {
                 throw new Error('Invalid frameId');
             }
             const useFrameOffsetForwarder = (parentPopupId === null);
-            ({id, depth, frameId} = await yomitan.crossFrame.invoke(frameId, 'PopupFactory.getOrCreatePopup', {
+            /** @type {{id: string, depth: number, frameId: number}} */
+            const info = await yomitan.crossFrame.invoke(frameId, 'PopupFactory.getOrCreatePopup', /** @type {import('popup-factory').GetOrCreatePopupDetails} */ ({
                 id,
                 parentPopupId,
                 frameId,
                 childrenSupported
             }));
+            id = info.id;
             const popup = new PopupProxy({
                 id,
-                depth,
-                frameId,
+                depth: info.depth,
+                frameId: info.frameId,
                 frameOffsetForwarder: useFrameOffsetForwarder ? this._frameOffsetForwarder : null
             });
             this._popups.set(id, popup);
@@ -172,24 +172,34 @@ export class PopupFactory {
      * Force all popups to have a specific visibility value.
      * @param {boolean} value Whether or not the popups should be visible.
      * @param {number} priority The priority of the override.
-     * @returns {string} A token which can be passed to clearAllVisibleOverride.
+     * @returns {Promise<import('core').TokenString>} A token which can be passed to clearAllVisibleOverride.
      * @throws An exception is thrown if any popup fails to have its visibiltiy overridden.
      */
     async setAllVisibleOverride(value, priority) {
         const promises = [];
-        const errors = [];
         for (const popup of this._popups.values()) {
-            const promise = popup.setVisibleOverride(value, priority)
-                .then(
-                    (token) => ({popup, token}),
-                    (error) => { errors.push(error); return null; }
-                );
+            const promise = this._setPopupVisibleOverrideReturnTuple(popup, value, priority);
             promises.push(promise);
         }
 
-        const results = (await Promise.all(promises)).filter(({token}) => token !== null);
+        /** @type {undefined|unknown} */
+        let error = void 0;
+        /** @type {{popup: import('popup').PopupAny, token: string}[]} */
+        const results = [];
+        for (const promise of promises) {
+            try {
+                const {popup, token} = await promise;
+                if (token !== null) {
+                    results.push({popup, token});
+                }
+            } catch (e) {
+                if (typeof error === 'undefined') {
+                    error = new Error(`Failed to set popup visibility override: ${e}`);
+                }
+            }
+        }
 
-        if (errors.length === 0) {
+        if (typeof error === 'undefined') {
             const token = generateId(16);
             this._allPopupVisibilityTokenMap.set(token, results);
             return token;
@@ -197,13 +207,24 @@ export class PopupFactory {
 
         // Revert on error
         await this._revertPopupVisibilityOverrides(results);
-        throw errors[0];
+        throw error;
+    }
+
+    /**
+     * @param {import('popup').PopupAny} popup
+     * @param {boolean} value
+     * @param {number} priority
+     * @returns {Promise<{popup: import('popup').PopupAny, token: ?string}>}
+     */
+    async _setPopupVisibleOverrideReturnTuple(popup, value, priority) {
+        const token = await popup.setVisibleOverride(value, priority);
+        return {popup, token};
     }
 
     /**
      * Clears a visibility override that was generated by `setAllVisibleOverride`.
-     * @param {string} token The token returned from `setAllVisibleOverride`.
-     * @returns {boolean} `true` if the override existed and was removed, `false` otherwise.
+     * @param {import('core').TokenString} token The token returned from `setAllVisibleOverride`.
+     * @returns {Promise<boolean>} `true` if the override existed and was removed, `false` otherwise.
      */
     async clearAllVisibleOverride(token) {
         const results = this._allPopupVisibilityTokenMap.get(token);
@@ -216,6 +237,10 @@ export class PopupFactory {
 
     // API message handlers
 
+    /**
+     * @param {import('popup-factory').GetOrCreatePopupDetails} details
+     * @returns {Promise<{id: string, depth: number, frameId: number}>}
+     */
     async _onApiGetOrCreatePopup(details) {
         const popup = await this.getOrCreatePopup(details);
         return {
@@ -225,31 +250,53 @@ export class PopupFactory {
         };
     }
 
+    /**
+     * @param {{id: string, optionsContext: import('settings').OptionsContext}} params
+     */
     async _onApiSetOptionsContext({id, optionsContext}) {
         const popup = this._getPopup(id);
-        return await popup.setOptionsContext(optionsContext);
+        await popup.setOptionsContext(optionsContext);
     }
 
-    _onApiHide({id, changeFocus}) {
+    /**
+     * @param {{id: string, changeFocus: boolean}} params
+     */
+    async _onApiHide({id, changeFocus}) {
         const popup = this._getPopup(id);
-        return popup.hide(changeFocus);
+        await popup.hide(changeFocus);
     }
 
+    /**
+     * @param {{id: string}} params
+     * @returns {Promise<boolean>}
+     */
     async _onApiIsVisibleAsync({id}) {
         const popup = this._getPopup(id);
         return await popup.isVisible();
     }
 
+    /**
+     * @param {{id: string, value: boolean, priority: number}} params
+     * @returns {Promise<?import('core').TokenString>}
+     */
     async _onApiSetVisibleOverride({id, value, priority}) {
         const popup = this._getPopup(id);
         return await popup.setVisibleOverride(value, priority);
     }
 
+    /**
+     * @param {{id: string, token: import('core').TokenString}} params
+     * @returns {Promise<boolean>}
+     */
     async _onApiClearVisibleOverride({id, token}) {
         const popup = this._getPopup(id);
         return await popup.clearVisibleOverride(token);
     }
 
+    /**
+     * @param {{id: string, x: number, y: number}} params
+     * @returns {Promise<boolean>}
+     */
     async _onApiContainsPoint({id, x, y}) {
         const popup = this._getPopup(id);
         const offset = this._getPopupOffset(popup);
@@ -258,6 +305,10 @@ export class PopupFactory {
         return await popup.containsPoint(x, y);
     }
 
+    /**
+     * @param {{id: string, details: import('popup').ContentDetails, displayDetails: ?import('display').ContentDetails}} params
+     * @returns {Promise<void>}
+     */
     async _onApiShowContent({id, details, displayDetails}) {
         const popup = this._getPopup(id);
         if (!this._popupCanShow(popup)) { return; }
@@ -274,36 +325,64 @@ export class PopupFactory {
         return await popup.showContent(details, displayDetails);
     }
 
-    _onApiSetCustomCss({id, css}) {
+    /**
+     * @param {{id: string, css: string}} params
+     * @returns {Promise<void>}
+     */
+    async _onApiSetCustomCss({id, css}) {
         const popup = this._getPopup(id);
-        return popup.setCustomCss(css);
+        await popup.setCustomCss(css);
     }
 
-    _onApiClearAutoPlayTimer({id}) {
+    /**
+     * @param {{id: string}} params
+     * @returns {Promise<void>}
+     */
+    async _onApiClearAutoPlayTimer({id}) {
         const popup = this._getPopup(id);
-        return popup.clearAutoPlayTimer();
+        await popup.clearAutoPlayTimer();
     }
 
-    _onApiSetContentScale({id, scale}) {
+    /**
+     * @param {{id: string, scale: number}} params
+     * @returns {Promise<void>}
+     */
+    async _onApiSetContentScale({id, scale}) {
         const popup = this._getPopup(id);
-        return popup.setContentScale(scale);
+        await popup.setContentScale(scale);
     }
 
-    _onApiUpdateTheme({id}) {
+    /**
+     * @param {{id: string}} params
+     * @returns {Promise<void>}
+     */
+    async _onApiUpdateTheme({id}) {
         const popup = this._getPopup(id);
-        return popup.updateTheme();
+        await popup.updateTheme();
     }
 
-    _onApiSetCustomOuterCss({id, css, useWebExtensionApi}) {
+    /**
+     * @param {{id: string, css: string, useWebExtensionApi: boolean}} params
+     * @returns {Promise<void>}
+     */
+    async _onApiSetCustomOuterCss({id, css, useWebExtensionApi}) {
         const popup = this._getPopup(id);
-        return popup.setCustomOuterCss(css, useWebExtensionApi);
+        await popup.setCustomOuterCss(css, useWebExtensionApi);
     }
 
+    /**
+     * @param {{id: string}} params
+     * @returns {Promise<import('popup').ValidSize>}
+     */
     async _onApiGetFrameSize({id}) {
         const popup = this._getPopup(id);
         return await popup.getFrameSize();
     }
 
+    /**
+     * @param {{id: string, width: number, height: number}} params
+     * @returns {Promise<boolean>}
+     */
     async _onApiSetFrameSize({id, width, height}) {
         const popup = this._getPopup(id);
         return await popup.setFrameSize(width, height);
@@ -311,6 +390,11 @@ export class PopupFactory {
 
     // Private functions
 
+    /**
+     * @param {string} id
+     * @returns {import('popup').PopupAny}
+     * @throws {Error}
+     */
     _getPopup(id) {
         const popup = this._popups.get(id);
         if (typeof popup === 'undefined') {
@@ -319,6 +403,10 @@ export class PopupFactory {
         return popup;
     }
 
+    /**
+     * @param {import('popup').PopupAny} popup
+     * @returns {{x: number, y: number}}
+     */
     _getPopupOffset(popup) {
         const {parent} = popup;
         if (parent !== null) {
@@ -330,11 +418,19 @@ export class PopupFactory {
         return {x: 0, y: 0};
     }
 
+    /**
+     * @param {import('popup').PopupAny} popup
+     * @returns {boolean}
+     */
     _popupCanShow(popup) {
         const parent = popup.parent;
         return parent === null || parent.isVisibleSync();
     }
 
+    /**
+     * @param {{popup: import('popup').PopupAny, token: string}[]} overrides
+     * @returns {Promise<boolean[]>}
+     */
     async _revertPopupVisibilityOverrides(overrides) {
         const promises = [];
         for (const value of overrides) {
diff --git a/ext/js/app/popup-proxy.js b/ext/js/app/popup-proxy.js
index 3d8b55ba..9b5b0214 100644
--- a/ext/js/app/popup-proxy.js
+++ b/ext/js/app/popup-proxy.js
@@ -24,15 +24,12 @@ import {Popup} from './popup.js';
 /**
  * This class is a proxy for a Popup that is hosted in a different frame.
  * It effectively forwards all API calls to the underlying Popup.
+ * @augments EventDispatcher<import('popup').PopupAnyEventType>
  */
 export class PopupProxy extends EventDispatcher {
     /**
      * Creates a new instance.
-     * @param {object} details Details about how to set up the instance.
-     * @param {string} details.id The ID of the popup.
-     * @param {number} details.depth The depth of the popup.
-     * @param {number} details.frameId The ID of the host frame.
-     * @param {FrameOffsetForwarder} details.frameOffsetForwarder A `FrameOffsetForwarder` instance which is used to determine frame positioning.
+     * @param {import('popup').PopupProxyConstructorDetails} details Details about how to set up the instance.
      */
     constructor({
         id,
@@ -41,15 +38,24 @@ export class PopupProxy extends EventDispatcher {
         frameOffsetForwarder
     }) {
         super();
+        /** @type {string} */
         this._id = id;
+        /** @type {number} */
         this._depth = depth;
+        /** @type {number} */
         this._frameId = frameId;
+        /** @type {?FrameOffsetForwarder} */
         this._frameOffsetForwarder = frameOffsetForwarder;
 
+        /** @type {number} */
         this._frameOffsetX = 0;
+        /** @type {number} */
         this._frameOffsetY = 0;
+        /** @type {?Promise<?[x: number, y: number]>} */
         this._frameOffsetPromise = null;
+        /** @type {?number} */
         this._frameOffsetUpdatedAt = null;
+        /** @type {number} */
         this._frameOffsetExpireTimeout = 1000;
     }
 
@@ -64,7 +70,7 @@ export class PopupProxy extends EventDispatcher {
     /**
      * The parent of the popup, which is always `null` for `PopupProxy` instances,
      * since any potential parent popups are in a different frame.
-     * @type {Popup}
+     * @type {?Popup}
      */
     get parent() {
         return null;
@@ -82,7 +88,7 @@ export class PopupProxy extends EventDispatcher {
     /**
      * The popup child popup, which is always null for `PopupProxy` instances,
      * since any potential child popups are in a different frame.
-     * @type {Popup}
+     * @type {?Popup}
      */
     get child() {
         return null;
@@ -99,7 +105,7 @@ export class PopupProxy extends EventDispatcher {
 
     /**
      * The depth of the popup.
-     * @type {numer}
+     * @type {number}
      */
     get depth() {
         return this._depth;
@@ -108,7 +114,7 @@ export class PopupProxy extends EventDispatcher {
     /**
      * Gets the content window of the frame. This value is null,
      * since the window is hosted in a different frame.
-     * @type {Window}
+     * @type {?Window}
      */
     get frameContentWindow() {
         return null;
@@ -116,7 +122,7 @@ export class PopupProxy extends EventDispatcher {
 
     /**
      * Gets the DOM node that contains the frame.
-     * @type {Element}
+     * @type {?Element}
      */
     get container() {
         return null;
@@ -132,11 +138,11 @@ export class PopupProxy extends EventDispatcher {
 
     /**
      * Sets the options context for the popup.
-     * @param {object} optionsContext The options context object.
+     * @param {import('settings').OptionsContext} optionsContext The options context object.
      * @returns {Promise<void>}
      */
-    setOptionsContext(optionsContext) {
-        return this._invokeSafe('PopupFactory.setOptionsContext', {id: this._id, optionsContext});
+    async setOptionsContext(optionsContext) {
+        await this._invokeSafe('PopupFactory.setOptionsContext', {id: this._id, optionsContext}, void 0);
     }
 
     /**
@@ -144,8 +150,8 @@ export class PopupProxy extends EventDispatcher {
      * @param {boolean} changeFocus Whether or not the parent popup or host frame should be focused.
      * @returns {Promise<void>}
      */
-    hide(changeFocus) {
-        return this._invokeSafe('PopupFactory.hide', {id: this._id, changeFocus});
+    async hide(changeFocus) {
+        await this._invokeSafe('PopupFactory.hide', {id: this._id, changeFocus}, void 0);
     }
 
     /**
@@ -160,7 +166,7 @@ export class PopupProxy extends EventDispatcher {
      * Force assigns the visibility of the popup.
      * @param {boolean} value Whether or not the popup should be visible.
      * @param {number} priority The priority of the override.
-     * @returns {Promise<string?>} A token used which can be passed to `clearVisibleOverride`,
+     * @returns {Promise<?import('core').TokenString>} A token used which can be passed to `clearVisibleOverride`,
      *   or null if the override wasn't assigned.
      */
     setVisibleOverride(value, priority) {
@@ -169,7 +175,7 @@ export class PopupProxy extends EventDispatcher {
 
     /**
      * Clears a visibility override that was generated by `setVisibleOverride`.
-     * @param {string} token The token returned from `setVisibleOverride`.
+     * @param {import('core').TokenString} token The token returned from `setVisibleOverride`.
      * @returns {Promise<boolean>} `true` if the override existed and was removed, `false` otherwise.
      */
     clearVisibleOverride(token) {
@@ -193,8 +199,8 @@ export class PopupProxy extends EventDispatcher {
 
     /**
      * Shows and updates the positioning and content of the popup.
-     * @param {Popup.ContentDetails} details Settings for the outer popup.
-     * @param {Display.ContentDetails} displayDetails The details parameter passed to `Display.setContent`.
+     * @param {import('popup').ContentDetails} details Settings for the outer popup.
+     * @param {?import('display').ContentDetails} displayDetails The details parameter passed to `Display.setContent`.
      * @returns {Promise<void>}
      */
     async showContent(details, displayDetails) {
@@ -208,7 +214,7 @@ export class PopupProxy extends EventDispatcher {
                 sourceRect.bottom += this._frameOffsetY;
             }
         }
-        return await this._invokeSafe('PopupFactory.showContent', {id: this._id, details, displayDetails});
+        await this._invokeSafe('PopupFactory.showContent', {id: this._id, details, displayDetails}, void 0);
     }
 
     /**
@@ -216,16 +222,16 @@ export class PopupProxy extends EventDispatcher {
      * @param {string} css The CSS rules.
      * @returns {Promise<void>}
      */
-    setCustomCss(css) {
-        return this._invokeSafe('PopupFactory.setCustomCss', {id: this._id, css});
+    async setCustomCss(css) {
+        await this._invokeSafe('PopupFactory.setCustomCss', {id: this._id, css}, void 0);
     }
 
     /**
      * Stops the audio auto-play timer, if one has started.
      * @returns {Promise<void>}
      */
-    clearAutoPlayTimer() {
-        return this._invokeSafe('PopupFactory.clearAutoPlayTimer', {id: this._id});
+    async clearAutoPlayTimer() {
+        await this._invokeSafe('PopupFactory.clearAutoPlayTimer', {id: this._id}, void 0);
     }
 
     /**
@@ -233,8 +239,8 @@ export class PopupProxy extends EventDispatcher {
      * @param {number} scale The scaling factor.
      * @returns {Promise<void>}
      */
-    setContentScale(scale) {
-        return this._invokeSafe('PopupFactory.setContentScale', {id: this._id, scale});
+    async setContentScale(scale) {
+        await this._invokeSafe('PopupFactory.setContentScale', {id: this._id, scale}, void 0);
     }
 
     /**
@@ -249,8 +255,8 @@ export class PopupProxy extends EventDispatcher {
      * Updates the outer theme of the popup.
      * @returns {Promise<void>}
      */
-    updateTheme() {
-        return this._invokeSafe('PopupFactory.updateTheme', {id: this._id});
+    async updateTheme() {
+        await this._invokeSafe('PopupFactory.updateTheme', {id: this._id}, void 0);
     }
 
     /**
@@ -260,13 +266,13 @@ export class PopupProxy extends EventDispatcher {
      *   When web extension APIs are used, a DOM node is not generated, making it harder to detect the changes.
      * @returns {Promise<void>}
      */
-    setCustomOuterCss(css, useWebExtensionApi) {
-        return this._invokeSafe('PopupFactory.setCustomOuterCss', {id: this._id, css, useWebExtensionApi});
+    async setCustomOuterCss(css, useWebExtensionApi) {
+        await this._invokeSafe('PopupFactory.setCustomOuterCss', {id: this._id, css, useWebExtensionApi}, void 0);
     }
 
     /**
      * Gets the rectangle of the DOM frame, synchronously.
-     * @returns {Popup.ValidRect} The rect.
+     * @returns {import('popup').ValidRect} The rect.
      *   `valid` is `false` for `PopupProxy`, since the DOM node is hosted in a different frame.
      */
     getFrameRect() {
@@ -275,7 +281,7 @@ export class PopupProxy extends EventDispatcher {
 
     /**
      * Gets the size of the DOM frame.
-     * @returns {Promise<{width: number, height: number, valid: boolean}>} The size and whether or not it is valid.
+     * @returns {Promise<import('popup').ValidSize>} The size and whether or not it is valid.
      */
     getFrameSize() {
         return this._invokeSafe('PopupFactory.getFrameSize', {id: this._id}, {width: 0, height: 0, valid: false});
@@ -288,16 +294,32 @@ export class PopupProxy extends EventDispatcher {
      * @returns {Promise<boolean>} `true` if the size assignment was successful, `false` otherwise.
      */
     setFrameSize(width, height) {
-        return this._invokeSafe('PopupFactory.setFrameSize', {id: this._id, width, height});
+        return this._invokeSafe('PopupFactory.setFrameSize', {id: this._id, width, height}, false);
     }
 
     // Private
 
-    _invoke(action, params={}) {
+    /**
+     * @template {import('core').SerializableObject} TParams
+     * @template [TReturn=unknown]
+     * @param {string} action
+     * @param {TParams} params
+     * @returns {Promise<TReturn>}
+     */
+    _invoke(action, params) {
         return yomitan.crossFrame.invoke(this._frameId, action, params);
     }
 
-    async _invokeSafe(action, params={}, defaultReturnValue) {
+    /**
+     * @template {import('core').SerializableObject} TParams
+     * @template [TReturn=unknown]
+     * @template [TReturnDefault=unknown]
+     * @param {string} action
+     * @param {TParams} params
+     * @param {TReturnDefault} defaultReturnValue
+     * @returns {Promise<TReturn|TReturnDefault>}
+     */
+    async _invokeSafe(action, params, defaultReturnValue) {
         try {
             return await this._invoke(action, params);
         } catch (e) {
@@ -306,10 +328,13 @@ export class PopupProxy extends EventDispatcher {
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _updateFrameOffset() {
         const now = Date.now();
         const firstRun = this._frameOffsetUpdatedAt === null;
-        const expired = firstRun || this._frameOffsetUpdatedAt < now - this._frameOffsetExpireTimeout;
+        const expired = firstRun || /** @type {number} */ (this._frameOffsetUpdatedAt) < now - this._frameOffsetExpireTimeout;
         if (this._frameOffsetPromise === null && !expired) { return; }
 
         if (this._frameOffsetPromise !== null) {
@@ -325,8 +350,11 @@ export class PopupProxy extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {number} now
+     */
     async _updateFrameOffsetInner(now) {
-        this._frameOffsetPromise = this._frameOffsetForwarder.getOffset();
+        this._frameOffsetPromise = /** @type {FrameOffsetForwarder} */ (this._frameOffsetForwarder).getOffset();
         try {
             const offset = await this._frameOffsetPromise;
             if (offset !== null) {
diff --git a/ext/js/app/popup-window.js b/ext/js/app/popup-window.js
index 88370684..af1ac1e4 100644
--- a/ext/js/app/popup-window.js
+++ b/ext/js/app/popup-window.js
@@ -22,14 +22,12 @@ import {Popup} from './popup.js';
 
 /**
  * This class represents a popup that is hosted in a new native window.
+ * @augments EventDispatcher<import('popup').PopupAnyEventType>
  */
 export class PopupWindow extends EventDispatcher {
     /**
      * Creates a new instance.
-     * @param {object} details Details about how to set up the instance.
-     * @param {string} details.id The ID of the popup.
-     * @param {number} details.depth The depth of the popup.
-     * @param {number} details.frameId The ID of the host frame.
+     * @param {import('popup').PopupWindowConstructorDetails} details Details about how to set up the instance.
      */
     constructor({
         id,
@@ -37,9 +35,13 @@ export class PopupWindow extends EventDispatcher {
         frameId
     }) {
         super();
+        /** @type {string} */
         this._id = id;
+        /** @type {number} */
         this._depth = depth;
+        /** @type {number} */
         this._frameId = frameId;
+        /** @type {?number} */
         this._popupTabId = null;
     }
 
@@ -51,6 +53,9 @@ export class PopupWindow extends EventDispatcher {
         return this._id;
     }
 
+    /**
+     * @type {?Popup}
+     */
     get parent() {
         return null;
     }
@@ -68,7 +73,7 @@ export class PopupWindow extends EventDispatcher {
     /**
      * The popup child popup, which is always null for `PopupWindow` instances,
      * since any potential child popups are in a different frame.
-     * @type {Popup}
+     * @type {?Popup}
      */
     get child() {
         return null;
@@ -85,7 +90,7 @@ export class PopupWindow extends EventDispatcher {
 
     /**
      * The depth of the popup.
-     * @type {numer}
+     * @type {number}
      */
     get depth() {
         return this._depth;
@@ -94,7 +99,7 @@ export class PopupWindow extends EventDispatcher {
     /**
      * Gets the content window of the frame. This value is null,
      * since the window is hosted in a different frame.
-     * @type {Window}
+     * @type {?Window}
      */
     get frameContentWindow() {
         return null;
@@ -102,7 +107,7 @@ export class PopupWindow extends EventDispatcher {
 
     /**
      * Gets the DOM node that contains the frame.
-     * @type {Element}
+     * @type {?Element}
      */
     get container() {
         return null;
@@ -118,11 +123,11 @@ export class PopupWindow extends EventDispatcher {
 
     /**
      * Sets the options context for the popup.
-     * @param {object} optionsContext The options context object.
+     * @param {import('settings').OptionsContext} optionsContext The options context object.
      * @returns {Promise<void>}
      */
-    setOptionsContext(optionsContext) {
-        return this._invoke(false, 'Display.setOptionsContext', {id: this._id, optionsContext});
+    async setOptionsContext(optionsContext) {
+        await this._invoke(false, 'Display.setOptionsContext', {id: this._id, optionsContext});
     }
 
     /**
@@ -145,7 +150,7 @@ export class PopupWindow extends EventDispatcher {
      * Force assigns the visibility of the popup.
      * @param {boolean} _value Whether or not the popup should be visible.
      * @param {number} _priority The priority of the override.
-     * @returns {Promise<string?>} A token used which can be passed to `clearVisibleOverride`,
+     * @returns {Promise<?import('core').TokenString>} A token used which can be passed to `clearVisibleOverride`,
      *   or null if the override wasn't assigned.
      */
     async setVisibleOverride(_value, _priority) {
@@ -154,10 +159,10 @@ export class PopupWindow extends EventDispatcher {
 
     /**
      * Clears a visibility override that was generated by `setVisibleOverride`.
-     * @param {string} _token The token returned from `setVisibleOverride`.
-     * @returns {boolean} `true` if the override existed and was removed, `false` otherwise.
+     * @param {import('core').TokenString} _token The token returned from `setVisibleOverride`.
+     * @returns {Promise<boolean>} `true` if the override existed and was removed, `false` otherwise.
      */
-    clearVisibleOverride(_token) {
+    async clearVisibleOverride(_token) {
         return false;
     }
 
@@ -173,8 +178,8 @@ export class PopupWindow extends EventDispatcher {
 
     /**
      * Shows and updates the positioning and content of the popup.
-     * @param {Popup.ContentDetails} _details Settings for the outer popup.
-     * @param {Display.ContentDetails} displayDetails The details parameter passed to `Display.setContent`.
+     * @param {import('popup').ContentDetails} _details Settings for the outer popup.
+     * @param {?import('display').ContentDetails} displayDetails The details parameter passed to `Display.setContent`.
      * @returns {Promise<void>}
      */
     async showContent(_details, displayDetails) {
@@ -187,23 +192,23 @@ export class PopupWindow extends EventDispatcher {
      * @param {string} css The CSS rules.
      * @returns {Promise<void>}
      */
-    setCustomCss(css) {
-        return this._invoke(false, 'Display.setCustomCss', {id: this._id, css});
+    async setCustomCss(css) {
+        await this._invoke(false, 'Display.setCustomCss', {id: this._id, css});
     }
 
     /**
      * Stops the audio auto-play timer, if one has started.
      * @returns {Promise<void>}
      */
-    clearAutoPlayTimer() {
-        return this._invoke(false, 'Display.clearAutoPlayTimer', {id: this._id});
+    async clearAutoPlayTimer() {
+        await this._invoke(false, 'Display.clearAutoPlayTimer', {id: this._id});
     }
 
     /**
      * Sets the scaling factor of the popup content.
      * @param {number} _scale The scaling factor.
      */
-    setContentScale(_scale) {
+    async setContentScale(_scale) {
         // NOP
     }
 
@@ -235,7 +240,7 @@ export class PopupWindow extends EventDispatcher {
 
     /**
      * Gets the rectangle of the DOM frame, synchronously.
-     * @returns {Popup.ValidRect} The rect.
+     * @returns {import('popup').ValidRect} The rect.
      *   `valid` is `false` for `PopupProxy`, since the DOM node is hosted in a different frame.
      */
     getFrameRect() {
@@ -244,7 +249,7 @@ export class PopupWindow extends EventDispatcher {
 
     /**
      * Gets the size of the DOM frame.
-     * @returns {Promise<{width: number, height: number, valid: boolean}>} The size and whether or not it is valid.
+     * @returns {Promise<import('popup').ValidSize>} The size and whether or not it is valid.
      */
     async getFrameSize() {
         return {width: 0, height: 0, valid: false};
@@ -262,9 +267,17 @@ export class PopupWindow extends EventDispatcher {
 
     // Private
 
-    async _invoke(open, action, params={}, defaultReturnValue) {
+    /**
+     * @template {import('core').SerializableObject} TParams
+     * @template [TReturn=unknown]
+     * @param {boolean} open
+     * @param {string} action
+     * @param {TParams} params
+     * @returns {Promise<TReturn|undefined>}
+     */
+    async _invoke(open, action, params) {
         if (yomitan.isExtensionUnloaded) {
-            return defaultReturnValue;
+            return void 0;
         }
 
         const frameId = 0;
@@ -280,7 +293,7 @@ export class PopupWindow extends EventDispatcher {
         }
 
         if (!open) {
-            return defaultReturnValue;
+            return void 0;
         }
 
         const {tabId} = await yomitan.api.getOrCreateSearchPopup({focus: 'ifCreated'});
diff --git a/ext/js/app/popup.js b/ext/js/app/popup.js
index 0e2e2493..31b18f01 100644
--- a/ext/js/app/popup.js
+++ b/ext/js/app/popup.js
@@ -25,53 +25,12 @@ import {ThemeController} from './theme-controller.js';
 
 /**
  * This class is the container which hosts the display of search results.
+ * @augments EventDispatcher<import('popup').PopupAnyEventType>
  */
 export class Popup extends EventDispatcher {
     /**
-     * Information about how popup content should be shown, specifically related to the outer popup frame.
-     * @typedef {object} ContentDetails
-     * @property {?object} optionsContext The options context for the content to show.
-     * @property {Rect[]} sourceRects The rectangles of the source content.
-     * @property {'horizontal-tb' | 'vertical-rl' | 'vertical-lr' | 'sideways-rl' | 'sideways-lr'} writingMode The normalized CSS writing-mode value of the source content.
-     */
-
-    /**
-     * A rectangle representing a DOM region, similar to DOMRect.
-     * @typedef {object} Rect
-     * @property {number} left The left position of the rectangle.
-     * @property {number} top The top position of the rectangle.
-     * @property {number} right The right position of the rectangle.
-     * @property {number} bottom The bottom position of the rectangle.
-     */
-
-    /**
-     * A rectangle representing a DOM region, similar to DOMRect but with a `valid` property.
-     * @typedef {object} ValidRect
-     * @property {number} left The left position of the rectangle.
-     * @property {number} top The top position of the rectangle.
-     * @property {number} right The right position of the rectangle.
-     * @property {number} bottom The bottom position of the rectangle.
-     * @property {boolean} valid Whether or not the rectangle is valid.
-     */
-
-    /**
-     * A rectangle representing a DOM region for placing the popup frame.
-     * @typedef {object} SizeRect
-     * @property {number} left The left position of the rectangle.
-     * @property {number} top The top position of the rectangle.
-     * @property {number} width The width of the rectangle.
-     * @property {number} height The height of the rectangle.
-     * @property {boolean} after Whether or not the rectangle is positioned to the right of the source rectangle.
-     * @property {boolean} below Whether or not the rectangle is positioned below the source rectangle.
-     */
-
-    /**
      * Creates a new instance.
-     * @param {object} details The details used to construct the new instance.
-     * @param {string} details.id The ID of the popup.
-     * @param {number} details.depth The depth of the popup.
-     * @param {number} details.frameId The ID of the host frame.
-     * @param {boolean} details.childrenSupported Whether or not the popup is able to show child popups.
+     * @param {import('popup').PopupConstructorDetails} details The details used to construct the new instance.
      */
     constructor({
         id,
@@ -80,48 +39,83 @@ export class Popup extends EventDispatcher {
         childrenSupported
     }) {
         super();
+        /** @type {string} */
         this._id = id;
+        /** @type {number} */
         this._depth = depth;
+        /** @type {number} */
         this._frameId = frameId;
+        /** @type {boolean} */
         this._childrenSupported = childrenSupported;
+        /** @type {?Popup} */
         this._parent = null;
+        /** @type {?Popup} */
         this._child = null;
+        /** @type {?Promise<boolean>} */
         this._injectPromise = null;
+        /** @type {boolean} */
         this._injectPromiseComplete = false;
+        /** @type {DynamicProperty<boolean>} */
         this._visible = new DynamicProperty(false);
+        /** @type {boolean} */
         this._visibleValue = false;
+        /** @type {?import('settings').OptionsContext} */
         this._optionsContext = null;
+        /** @type {number} */
         this._contentScale = 1.0;
+        /** @type {string} */
         this._targetOrigin = chrome.runtime.getURL('/').replace(/\/$/, '');
 
-        this._optionsAssigned = false;
+        /** @type {number} */
         this._initialWidth = 400;
+        /** @type {number} */
         this._initialHeight = 250;
+        /** @type {number} */
         this._horizontalOffset = 0;
+        /** @type {number} */
         this._verticalOffset = 10;
+        /** @type {number} */
         this._horizontalOffset2 = 10;
+        /** @type {number} */
         this._verticalOffset2 = 0;
+        /** @type {import('settings').PopupVerticalTextPosition} */
         this._verticalTextPosition = 'before';
+        /** @type {boolean} */
         this._horizontalTextPositionBelow = true;
+        /** @type {import('settings').PopupDisplayMode} */
         this._displayMode = 'default';
+        /** @type {boolean} */
         this._displayModeIsFullWidth = false;
+        /** @type {boolean} */
         this._scaleRelativeToVisualViewport = true;
+        /** @type {boolean} */
         this._useSecureFrameUrl = true;
+        /** @type {boolean} */
         this._useShadowDom = true;
+        /** @type {string} */
         this._customOuterCss = '';
 
+        /** @type {?number} */
         this._frameSizeContentScale = null;
+        /** @type {?FrameClient} */
         this._frameClient = null;
+        /** @type {HTMLIFrameElement} */
         this._frame = document.createElement('iframe');
         this._frame.className = 'yomitan-popup';
         this._frame.style.width = '0';
         this._frame.style.height = '0';
+        /** @type {boolean} */
+        this._frameConnected = false;
 
+        /** @type {HTMLElement} */
         this._container = this._frame;
+        /** @type {?ShadowRoot} */
         this._shadow = null;
 
+        /** @type {ThemeController} */
         this._themeController = new ThemeController(this._frame);
 
+        /** @type {EventListenerCollection} */
         this._fullscreenEventListeners = new EventListenerCollection();
     }
 
@@ -135,7 +129,7 @@ export class Popup extends EventDispatcher {
 
     /**
      * The parent of the popup.
-     * @type {Popup}
+     * @type {?Popup}
      */
     get parent() {
         return this._parent;
@@ -151,7 +145,7 @@ export class Popup extends EventDispatcher {
 
     /**
      * The child of the popup.
-     * @type {Popup}
+     * @type {?Popup}
      */
     get child() {
         return this._child;
@@ -167,7 +161,7 @@ export class Popup extends EventDispatcher {
 
     /**
      * The depth of the popup.
-     * @type {numer}
+     * @type {number}
      */
     get depth() {
         return this._depth;
@@ -215,11 +209,13 @@ export class Popup extends EventDispatcher {
 
     /**
      * Sets the options context for the popup.
-     * @param {object} optionsContext The options context object.
+     * @param {import('settings').OptionsContext} optionsContext The options context object.
      */
     async setOptionsContext(optionsContext) {
         await this._setOptionsContext(optionsContext);
-        await this._invokeSafe('Display.setOptionsContext', {optionsContext});
+        if (this._frameConnected) {
+            await this._invokeSafe('Display.setOptionsContext', {optionsContext});
+        }
     }
 
     /**
@@ -252,7 +248,7 @@ export class Popup extends EventDispatcher {
      * Force assigns the visibility of the popup.
      * @param {boolean} value Whether or not the popup should be visible.
      * @param {number} priority The priority of the override.
-     * @returns {Promise<string?>} A token used which can be passed to `clearVisibleOverride`,
+     * @returns {Promise<?import('core').TokenString>} A token used which can be passed to `clearVisibleOverride`,
      *   or null if the override wasn't assigned.
      */
     async setVisibleOverride(value, priority) {
@@ -261,7 +257,7 @@ export class Popup extends EventDispatcher {
 
     /**
      * Clears a visibility override that was generated by `setVisibleOverride`.
-     * @param {string} token The token returned from `setVisibleOverride`.
+     * @param {import('core').TokenString} token The token returned from `setVisibleOverride`.
      * @returns {Promise<boolean>} `true` if the override existed and was removed, `false` otherwise.
      */
     async clearVisibleOverride(token) {
@@ -275,7 +271,8 @@ export class Popup extends EventDispatcher {
      * @returns {Promise<boolean>} `true` if the point is contained within the popup's rect, `false` otherwise.
      */
     async containsPoint(x, y) {
-        for (let popup = this; popup !== null && popup.isVisibleSync(); popup = popup.child) {
+        // eslint-disable-next-line @typescript-eslint/no-this-alias
+        for (let popup = /** @type {?Popup} */ (this); popup !== null && popup.isVisibleSync(); popup = popup.child) {
             const rect = popup.getFrameRect();
             if (rect.valid && x >= rect.left && y >= rect.top && x < rect.right && y < rect.bottom) {
                 return true;
@@ -286,12 +283,12 @@ export class Popup extends EventDispatcher {
 
     /**
      * Shows and updates the positioning and content of the popup.
-     * @param {ContentDetails} details Settings for the outer popup.
-     * @param {Display.ContentDetails} displayDetails The details parameter passed to `Display.setContent`.
+     * @param {import('popup').ContentDetails} details Settings for the outer popup.
+     * @param {?import('display').ContentDetails} displayDetails The details parameter passed to `Display.setContent`.
      * @returns {Promise<void>}
      */
     async showContent(details, displayDetails) {
-        if (!this._optionsAssigned) { throw new Error('Options not assigned'); }
+        if (this._optionsContext === null) { throw new Error('Options not assigned'); }
 
         const {optionsContext, sourceRects, writingMode} = details;
         if (optionsContext !== null) {
@@ -309,25 +306,27 @@ export class Popup extends EventDispatcher {
      * Sets the custom styles for the popup content.
      * @param {string} css The CSS rules.
      */
-    setCustomCss(css) {
-        this._invokeSafe('Display.setCustomCss', {css});
+    async setCustomCss(css) {
+        await this._invokeSafe('Display.setCustomCss', {css});
     }
 
     /**
      * Stops the audio auto-play timer, if one has started.
      */
-    clearAutoPlayTimer() {
-        this._invokeSafe('Display.clearAutoPlayTimer');
+    async clearAutoPlayTimer() {
+        if (this._frameConnected) {
+            await this._invokeSafe('Display.clearAutoPlayTimer', {});
+        }
     }
 
     /**
      * Sets the scaling factor of the popup content.
      * @param {number} scale The scaling factor.
      */
-    setContentScale(scale) {
+    async setContentScale(scale) {
         this._contentScale = scale;
         this._frame.style.fontSize = `${scale}px`;
-        this._invokeSafe('Display.setContentScale', {scale});
+        await this._invokeSafe('Display.setContentScale', {scale});
     }
 
     /**
@@ -360,12 +359,14 @@ export class Popup extends EventDispatcher {
             parentNode = this._shadow;
         }
         const node = await dynamicLoader.loadStyle('yomitan-popup-outer-user-stylesheet', 'code', css, useWebExtensionApi, parentNode);
-        this.trigger('customOuterCssChanged', {node, useWebExtensionApi, inShadow});
+        /** @type {import('popup').CustomOuterCssChangedEvent} */
+        const event = {node, useWebExtensionApi, inShadow};
+        this.trigger('customOuterCssChanged', event);
     }
 
     /**
      * Gets the rectangle of the DOM frame, synchronously.
-     * @returns {ValidRect} The rect.
+     * @returns {import('popup').ValidRect} The rect.
      *   `valid` is `false` for `PopupProxy`, since the DOM node is hosted in a different frame.
      */
     getFrameRect() {
@@ -375,7 +376,7 @@ export class Popup extends EventDispatcher {
 
     /**
      * Gets the size of the DOM frame.
-     * @returns {Promise<{width: number, height: number, valid: boolean}>} The size and whether or not it is valid.
+     * @returns {Promise<import('popup').ValidSize>} The size and whether or not it is valid.
      */
     async getFrameSize() {
         const {width, height} = this._getFrameBoundingClientRect();
@@ -395,14 +396,23 @@ export class Popup extends EventDispatcher {
 
     // Private functions
 
+    /**
+     * @returns {void}
+     */
     _onFrameMouseOver() {
         this.trigger('framePointerOver', {});
     }
 
+    /**
+     * @returns {void}
+     */
     _onFrameMouseOut() {
         this.trigger('framePointerOut', {});
     }
 
+    /**
+     * @returns {Promise<boolean>}
+     */
     _inject() {
         let injectPromise = this._injectPromise;
         if (injectPromise === null) {
@@ -419,19 +429,25 @@ export class Popup extends EventDispatcher {
         return injectPromise;
     }
 
+    /**
+     * @returns {Promise<boolean>}
+     */
     async _injectInner1() {
         try {
             await this._injectInner2();
             return true;
         } catch (e) {
             this._resetFrame();
-            if (e.source === this) { return false; } // Passive error
+            if (e instanceof PopupError && e.source === this) { return false; } // Passive error
             throw e;
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _injectInner2() {
-        if (!this._optionsAssigned) {
+        if (this._optionsContext === null) {
             throw new Error('Options not initialized');
         }
 
@@ -439,6 +455,7 @@ export class Popup extends EventDispatcher {
 
         await this._setUpContainer(this._useShadowDom);
 
+        /** @type {import('frame-client').SetupFrameFunction} */
         const setupFrame = (frame) => {
             frame.removeAttribute('src');
             frame.removeAttribute('srcdoc');
@@ -447,9 +464,8 @@ export class Popup extends EventDispatcher {
             const {contentDocument} = frame;
             if (contentDocument === null) {
                 // This can occur when running inside a sandboxed frame without "allow-same-origin"
-                const error = new Error('Popup not supoprted in this context');
-                error.source = this; // Used to detect a passive error which should be ignored
-                throw error;
+                // Custom error is used to detect a passive error which should be ignored
+                throw new PopupError('Popup not supported in this context', this);
             }
             const url = chrome.runtime.getURL('/popup.html');
             if (useSecurePopupFrameUrl) {
@@ -462,23 +478,32 @@ export class Popup extends EventDispatcher {
         const frameClient = new FrameClient();
         this._frameClient = frameClient;
         await frameClient.connect(this._frame, this._targetOrigin, this._frameId, setupFrame);
+        this._frameConnected = true;
 
         // Configure
-        await this._invokeSafe('Display.configure', {
+        /** @type {import('display').ConfigureMessageDetails} */
+        const configureParams = {
             depth: this._depth,
             parentPopupId: this._id,
             parentFrameId: this._frameId,
             childrenSupported: this._childrenSupported,
             scale: this._contentScale,
             optionsContext: this._optionsContext
-        });
+        };
+        await this._invokeSafe('Display.configure', configureParams);
     }
 
+    /**
+     * @returns {void}
+     */
     _onFrameLoad() {
         if (!this._injectPromiseComplete) { return; }
         this._resetFrame();
     }
 
+    /**
+     * @returns {void}
+     */
     _resetFrame() {
         const parent = this._container.parentNode;
         if (parent !== null) {
@@ -488,10 +513,14 @@ export class Popup extends EventDispatcher {
         this._frame.removeAttribute('srcdoc');
 
         this._frameClient = null;
+        this._frameConnected = false;
         this._injectPromise = null;
         this._injectPromiseComplete = false;
     }
 
+    /**
+     * @param {boolean} usePopupShadowDom
+     */
     async _setUpContainer(usePopupShadowDom) {
         if (usePopupShadowDom && typeof this._frame.attachShadow === 'function') {
             const container = document.createElement('div');
@@ -514,6 +543,9 @@ export class Popup extends EventDispatcher {
         await this._injectStyles();
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _injectStyles() {
         try {
             await this._injectPopupOuterStylesheet();
@@ -528,7 +560,11 @@ export class Popup extends EventDispatcher {
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _injectPopupOuterStylesheet() {
+        /** @type {'code'|'file'|'file-content'} */
         let fileType = 'file';
         let useWebExtensionApi = true;
         let parentNode = null;
@@ -540,6 +576,9 @@ export class Popup extends EventDispatcher {
         await dynamicLoader.loadStyle('yomitan-popup-outer-stylesheet', fileType, '/css/popup-outer.css', useWebExtensionApi, parentNode);
     }
 
+    /**
+     * @param {boolean} observe
+     */
     _observeFullscreen(observe) {
         if (!observe) {
             this._fullscreenEventListeners.removeAllEventListeners();
@@ -554,6 +593,9 @@ export class Popup extends EventDispatcher {
         DocumentUtil.addFullscreenChangeEventListener(this._onFullscreenChanged.bind(this), this._fullscreenEventListeners);
     }
 
+    /**
+     * @returns {void}
+     */
     _onFullscreenChanged() {
         const parent = this._getFrameParentElement();
         if (parent !== null && this._container.parentNode !== parent) {
@@ -561,6 +603,10 @@ export class Popup extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {import('popup').Rect[]} sourceRects
+     * @param {import('document-util').NormalizedWritingMode} writingMode
+     */
     async _show(sourceRects, writingMode) {
         const injected = await this._inject();
         if (!injected) { return; }
@@ -588,16 +634,26 @@ export class Popup extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {number} width
+     * @param {number} height
+     */
     _setFrameSize(width, height) {
         const {style} = this._frame;
         style.width = `${width}px`;
         style.height = `${height}px`;
     }
 
+    /**
+     * @param {boolean} visible
+     */
     _setVisible(visible) {
         this._visible.defaultValue = visible;
     }
 
+    /**
+     * @param {import('dynamic-property').ChangeEventDetails<boolean>} event
+     */
     _onVisibleChange({value}) {
         if (this._visibleValue === value) { return; }
         this._visibleValue = value;
@@ -605,6 +661,9 @@ export class Popup extends EventDispatcher {
         this._invokeSafe('Display.visibilityChanged', {value});
     }
 
+    /**
+     * @returns {void}
+     */
     _focusParent() {
         if (this._parent !== null) {
             // Chrome doesn't like focusing iframe without contentWindow.
@@ -621,23 +680,43 @@ export class Popup extends EventDispatcher {
         }
     }
 
-    async _invoke(action, params={}) {
+    /**
+     * @template {import('core').SerializableObject} TParams
+     * @template [TReturn=unknown]
+     * @param {string} action
+     * @param {TParams} params
+     * @returns {Promise<TReturn>}
+     */
+    async _invoke(action, params) {
         const contentWindow = this._frame.contentWindow;
-        if (this._frameClient === null || !this._frameClient.isConnected() || contentWindow === null) { return; }
+        if (this._frameClient === null || !this._frameClient.isConnected() || contentWindow === null) {
+            throw new Error(`Failed to invoke action ${action}: frame state invalid`);
+        }
 
         const message = this._frameClient.createMessage({action, params});
         return await yomitan.crossFrame.invoke(this._frameClient.frameId, 'popupMessage', message);
     }
 
-    async _invokeSafe(action, params={}, defaultReturnValue) {
+    /**
+     * @template {import('core').SerializableObject} TParams
+     * @template [TReturn=unknown]
+     * @param {string} action
+     * @param {TParams} params
+     * @returns {Promise<TReturn|undefined>}
+     */
+    async _invokeSafe(action, params) {
         try {
             return await this._invoke(action, params);
         } catch (e) {
             if (!yomitan.isExtensionUnloaded) { throw e; }
-            return defaultReturnValue;
+            return void 0;
         }
     }
 
+    /**
+     * @param {string} action
+     * @param {import('core').SerializableObject} params
+     */
     _invokeWindow(action, params={}) {
         const contentWindow = this._frame.contentWindow;
         if (this._frameClient === null || !this._frameClient.isConnected() || contentWindow === null) { return; }
@@ -646,10 +725,16 @@ export class Popup extends EventDispatcher {
         contentWindow.postMessage(message, this._targetOrigin);
     }
 
+    /**
+     * @returns {void}
+     */
     _onExtensionUnloaded() {
         this._invokeWindow('Display.extensionUnloaded');
     }
 
+    /**
+     * @returns {Element}
+     */
     _getFrameParentElement() {
         let defaultParent = document.body;
         if (defaultParent !== null && defaultParent.tagName.toLowerCase() === 'frameset') {
@@ -659,7 +744,8 @@ export class Popup extends EventDispatcher {
         if (
             fullscreenElement === null ||
             fullscreenElement.shadowRoot ||
-            fullscreenElement.openOrClosedShadowRoot // Available to Firefox 63+ for WebExtensions
+            // @ts-ignore - openOrClosedShadowRoot is available to Firefox 63+ for WebExtensions
+            fullscreenElement.openOrClosedShadowRoot
         ) {
             return defaultParent;
         }
@@ -675,10 +761,10 @@ export class Popup extends EventDispatcher {
 
     /**
      * Computes the position where the popup should be placed relative to the source content.
-     * @param {Rect[]} sourceRects The rectangles of the source content.
-     * @param {string} writingMode The CSS writing mode of the source text.
-     * @param {Rect} viewport The viewport that the popup can be placed within.
-     * @returns {SizeRect} The calculated rectangle for where to position the popup.
+     * @param {import('popup').Rect[]} sourceRects The rectangles of the source content.
+     * @param {import('document-util').NormalizedWritingMode} writingMode The CSS writing mode of the source text.
+     * @param {import('popup').Rect} viewport The viewport that the popup can be placed within.
+     * @returns {import('popup').SizeRect} The calculated rectangle for where to position the popup.
      */
     _getPosition(sourceRects, writingMode, viewport) {
         sourceRects = this._convertSourceRectsCoordinateSpace(sourceRects);
@@ -705,6 +791,7 @@ export class Popup extends EventDispatcher {
         horizontalOffset *= contentScale;
         verticalOffset *= contentScale;
 
+        /** @type {?import('popup').SizeRect} */
         let best = null;
         const sourceRectsLength = sourceRects.length;
         for (let i = 0, ii = (sourceRectsLength > 1 ? sourceRectsLength : 0); i <= ii; ++i) {
@@ -720,19 +807,20 @@ export class Popup extends EventDispatcher {
                 if (result.height >= frameHeight) { break; }
             }
         }
-        return best;
+        // Given the loop conditions, this is guaranteed to be non-null
+        return /** @type {import('popup').SizeRect} */ (best);
     }
 
     /**
      * Computes the position where the popup should be placed for horizontal text.
-     * @param {Rect} sourceRect The rectangle of the source content.
+     * @param {import('popup').Rect} sourceRect The rectangle of the source content.
      * @param {number} frameWidth The preferred width of the frame.
      * @param {number} frameHeight The preferred height of the frame.
-     * @param {Rect} viewport The viewport that the frame can be placed within.
+     * @param {import('popup').Rect} viewport The viewport that the frame can be placed within.
      * @param {number} horizontalOffset The horizontal offset from the source rect that the popup will be placed.
      * @param {number} verticalOffset The vertical offset from the source rect that the popup will be placed.
      * @param {boolean} preferBelow Whether or not the popup is preferred to be placed below the source content.
-     * @returns {SizeRect} The calculated rectangle for where to position the popup.
+     * @returns {import('popup').SizeRect} The calculated rectangle for where to position the popup.
      */
     _getPositionForHorizontalText(sourceRect, frameWidth, frameHeight, viewport, horizontalOffset, verticalOffset, preferBelow) {
         const [left, width, after] = this._getConstrainedPosition(
@@ -756,14 +844,14 @@ export class Popup extends EventDispatcher {
 
     /**
      * Computes the position where the popup should be placed for vertical text.
-     * @param {Rect} sourceRect The rectangle of the source content.
+     * @param {import('popup').Rect} sourceRect The rectangle of the source content.
      * @param {number} frameWidth The preferred width of the frame.
      * @param {number} frameHeight The preferred height of the frame.
-     * @param {Rect} viewport The viewport that the frame can be placed within.
+     * @param {import('popup').Rect} viewport The viewport that the frame can be placed within.
      * @param {number} horizontalOffset The horizontal offset from the source rect that the popup will be placed.
      * @param {number} verticalOffset The vertical offset from the source rect that the popup will be placed.
      * @param {boolean} preferRight Whether or not the popup is preferred to be placed to the right of the source content.
-     * @returns {SizeRect} The calculated rectangle for where to position the popup.
+     * @returns {import('popup').SizeRect} The calculated rectangle for where to position the popup.
      */
     _getPositionForVerticalText(sourceRect, frameWidth, frameHeight, viewport, horizontalOffset, verticalOffset, preferRight) {
         const [left, width, after] = this._getConstrainedPositionBinary(
@@ -785,6 +873,11 @@ export class Popup extends EventDispatcher {
         return {left, top, width, height, after, below};
     }
 
+    /**
+     * @param {import('settings').PopupVerticalTextPosition} positionPreference
+     * @param {import('document-util').NormalizedWritingMode} writingMode
+     * @returns {boolean}
+     */
     _isVerticalTextPopupOnRight(positionPreference, writingMode) {
         switch (positionPreference) {
             case 'before':
@@ -799,6 +892,10 @@ export class Popup extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {import('document-util').NormalizedWritingMode} writingMode
+     * @returns {boolean}
+     */
     _isWritingModeLeftToRight(writingMode) {
         switch (writingMode) {
             case 'vertical-lr':
@@ -809,6 +906,15 @@ export class Popup extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {number} positionBefore
+     * @param {number} positionAfter
+     * @param {number} size
+     * @param {number} minLimit
+     * @param {number} maxLimit
+     * @param {boolean} after
+     * @returns {[position: number, size: number, after: boolean]}
+     */
     _getConstrainedPosition(positionBefore, positionAfter, size, minLimit, maxLimit, after) {
         size = Math.min(size, maxLimit - minLimit);
 
@@ -824,6 +930,15 @@ export class Popup extends EventDispatcher {
         return [position, size, after];
     }
 
+    /**
+     * @param {number} positionBefore
+     * @param {number} positionAfter
+     * @param {number} size
+     * @param {number} minLimit
+     * @param {number} maxLimit
+     * @param {boolean} after
+     * @returns {[position: number, size: number, after: boolean]}
+     */
     _getConstrainedPositionBinary(positionBefore, positionAfter, size, minLimit, maxLimit, after) {
         const overflowBefore = minLimit - (positionBefore - size);
         const overflowAfter = (positionAfter + size) - maxLimit;
@@ -847,11 +962,11 @@ export class Popup extends EventDispatcher {
     /**
      * Gets the visual viewport.
      * @param {boolean} useVisualViewport Whether or not the `window.visualViewport` should be used.
-     * @returns {Rect} The rectangle of the visual viewport.
+     * @returns {import('popup').Rect} The rectangle of the visual viewport.
      */
     _getViewport(useVisualViewport) {
-        const visualViewport = window.visualViewport;
-        if (visualViewport !== null && typeof visualViewport === 'object') {
+        const {visualViewport} = window;
+        if (typeof visualViewport !== 'undefined' && visualViewport !== null) {
             const left = visualViewport.offsetLeft;
             const top = visualViewport.offsetTop;
             const width = visualViewport.width;
@@ -882,6 +997,9 @@ export class Popup extends EventDispatcher {
         };
     }
 
+    /**
+     * @param {import('settings').OptionsContext} optionsContext
+     */
     async _setOptionsContext(optionsContext) {
         this._optionsContext = optionsContext;
         const options = await yomitan.api.optionsGet(optionsContext);
@@ -902,10 +1020,12 @@ export class Popup extends EventDispatcher {
         this._useSecureFrameUrl = general.useSecurePopupFrameUrl;
         this._useShadowDom = general.usePopupShadowDom;
         this._customOuterCss = general.customPopupOuterCss;
-        this._optionsAssigned = true;
         this.updateTheme();
     }
 
+    /**
+     * @param {import('settings').OptionsContext} optionsContext
+     */
     async _setOptionsContextIfDifferent(optionsContext) {
         if (deepEqual(this._optionsContext, optionsContext)) { return; }
         await this._setOptionsContext(optionsContext);
@@ -913,8 +1033,8 @@ export class Popup extends EventDispatcher {
 
     /**
      * Computes the bounding rectangle for a set of rectangles.
-     * @param {Rect[]} sourceRects An array of rectangles.
-     * @returns {Rect} The bounding rectangle for all of the source rectangles.
+     * @param {import('popup').Rect[]} sourceRects An array of rectangles.
+     * @returns {import('popup').Rect} The bounding rectangle for all of the source rectangles.
      */
     _getBoundingSourceRect(sourceRects) {
         switch (sourceRects.length) {
@@ -934,8 +1054,8 @@ export class Popup extends EventDispatcher {
 
     /**
      * Checks whether or not a rectangle is overlapping any other rectangles.
-     * @param {SizeRect} sizeRect The rectangles to check for overlaps.
-     * @param {Rect[]} sourceRects The list of rectangles to compare against.
+     * @param {import('popup').SizeRect} sizeRect The rectangles to check for overlaps.
+     * @param {import('popup').Rect[]} sourceRects The list of rectangles to compare against.
      * @param {number} ignoreIndex The index of an item in `sourceRects` to ignore.
      * @returns {boolean} `true` if `sizeRect` overlaps any one of `sourceRects`, excluding `sourceRects[ignoreIndex]`; `false` otherwise.
      */
@@ -968,8 +1088,8 @@ export class Popup extends EventDispatcher {
 
     /**
      * Converts the coordinate space of source rectangles.
-     * @param {Rect[]} sourceRects The list of rectangles to convert.
-     * @returns {Rect[]} Either an updated list of rectangles, or `sourceRects` if no change is required.
+     * @param {import('popup').Rect[]} sourceRects The list of rectangles to convert.
+     * @returns {import('popup').Rect[]} Either an updated list of rectangles, or `sourceRects` if no change is required.
      */
     _convertSourceRectsCoordinateSpace(sourceRects) {
         let scale = DocumentUtil.computeZoomScale(this._container);
@@ -984,9 +1104,9 @@ export class Popup extends EventDispatcher {
 
     /**
      * Creates a scaled rectangle.
-     * @param {Rect} rect The rectangle to scale.
+     * @param {import('popup').Rect} rect The rectangle to scale.
      * @param {number} scale The scale factor.
-     * @returns {Rect} A new rectangle which has been scaled.
+     * @returns {import('popup').Rect} A new rectangle which has been scaled.
      */
     _createScaledRect(rect, scale) {
         return {
@@ -997,3 +1117,18 @@ export class Popup extends EventDispatcher {
         };
     }
 }
+
+class PopupError extends ExtensionError {
+    /**
+     * @param {string} message
+     * @param {Popup} source
+     */
+    constructor(message, source) {
+        super(message);
+        /** @type {Popup} */
+        this._source = source;
+    }
+
+    /** @type {Popup} */
+    get source() { return this._source; }
+}
diff --git a/ext/js/app/theme-controller.js b/ext/js/app/theme-controller.js
index f403a534..8b88c834 100644
--- a/ext/js/app/theme-controller.js
+++ b/ext/js/app/theme-controller.js
@@ -22,13 +22,18 @@
 export class ThemeController {
     /**
      * Creates a new instance of the class.
-     * @param {?Element} element A DOM element which theme properties are applied to.
+     * @param {?HTMLElement} element A DOM element which theme properties are applied to.
      */
     constructor(element) {
+        /** @type {?HTMLElement} */
         this._element = element;
-        this._theme = 'default';
-        this._outerTheme = 'default';
+        /** @type {'light'|'dark'|'browser'} */
+        this._theme = 'light';
+        /** @type {'light'|'dark'|'browser'|'site'} */
+        this._outerTheme = 'light';
+        /** @type {?('dark'|'light')} */
         this._siteTheme = null;
+        /** @type {'dark'|'light'} */
         this._browserTheme = 'light';
     }
 
@@ -42,7 +47,7 @@ export class ThemeController {
 
     /**
      * Sets the DOM element which theme properties are applied to.
-     * @param {?Element} value The DOM element to assign.
+     * @param {?HTMLElement} value The DOM element to assign.
      */
     set element(value) {
         this._element = value;
@@ -50,7 +55,7 @@ export class ThemeController {
 
     /**
      * Gets the main theme for the content.
-     * @type {string}
+     * @type {'light'|'dark'|'browser'}
      */
     get theme() {
         return this._theme;
@@ -58,7 +63,7 @@ export class ThemeController {
 
     /**
      * Sets the main theme for the content.
-     * @param {string} value The theme value to assign.
+     * @param {'light'|'dark'|'browser'} value The theme value to assign.
      */
     set theme(value) {
         this._theme = value;
@@ -66,7 +71,7 @@ export class ThemeController {
 
     /**
      * Gets the outer theme for the content.
-     * @type {string}
+     * @type {'light'|'dark'|'browser'|'site'}
      */
     get outerTheme() {
         return this._outerTheme;
@@ -74,7 +79,7 @@ export class ThemeController {
 
     /**
      * Sets the outer theme for the content.
-     * @param {string} value The outer theme value to assign.
+     * @param {'light'|'dark'|'browser'|'site'} value The outer theme value to assign.
      */
     set outerTheme(value) {
         this._outerTheme = value;
@@ -83,7 +88,7 @@ export class ThemeController {
     /**
      * Gets the override value for the site theme.
      * If this value is `null`, the computed value will be used.
-     * @type {?string}
+     * @type {?('dark'|'light')}
      */
     get siteTheme() {
         return this._siteTheme;
@@ -92,7 +97,7 @@ export class ThemeController {
     /**
      * Sets the override value for the site theme.
      * If this value is `null`, the computed value will be used.
-     * @param {?string} value The site theme value to assign.
+     * @param {?('dark'|'light')} value The site theme value to assign.
      */
     set siteTheme(value) {
         this._siteTheme = value;
@@ -101,7 +106,7 @@ export class ThemeController {
     /**
      * Gets the browser's preferred color theme.
      * The value can be either 'light' or 'dark'.
-     * @type {?string}
+     * @type {'dark'|'light'}
      */
     get browserTheme() {
         return this._browserTheme;
@@ -152,7 +157,6 @@ export class ThemeController {
     /**
      * Event handler for when the preferred browser theme changes.
      * @param {MediaQueryList|MediaQueryListEvent} detail The object containing event details.
-     * @param {boolean} detail.matches The object containing event details.
      */
     _onPrefersColorSchemeDarkChange({matches}) {
         this._browserTheme = (matches ? 'dark' : 'light');