Simplify message handlers (#396)

14 files changed, 127 insertions, 145 deletions

diff --git a/ext/js/app/frontend.js b/ext/js/app/frontend.js
index a1bbb217..8c11775a 100644
--- a/ext/js/app/frontend.js
+++ b/ext/js/app/frontend.js
@@ -108,10 +108,10 @@ export class Frontend {
 
         /* eslint-disable no-multi-spaces */
         /** @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._runtimeMessageHandlers = new Map(/** @type {import('core').MessageHandlerMapInit} */ ([
+            ['Frontend.requestReadyBroadcast',   this._onMessageRequestFrontendReadyBroadcast.bind(this)],
+            ['Frontend.setAllVisibleOverride',   this._onApiSetAllVisibleOverride.bind(this)],
+            ['Frontend.clearAllVisibleOverride', this._onApiClearAllVisibleOverride.bind(this)]
         ]));
 
         this._hotkeyHandler.registerActions([
@@ -178,11 +178,11 @@ export class Frontend {
 
         /* eslint-disable no-multi-spaces */
         yomitan.crossFrame.registerHandlers([
-            ['Frontend.closePopup',       {async: false, handler: this._onApiClosePopup.bind(this)}],
-            ['Frontend.copySelection',    {async: false, handler: this._onApiCopySelection.bind(this)}],
-            ['Frontend.getSelectionText', {async: false, handler: this._onApiGetSelectionText.bind(this)}],
-            ['Frontend.getPopupInfo',     {async: false, handler: this._onApiGetPopupInfo.bind(this)}],
-            ['Frontend.getPageInfo',      {async: false, handler: this._onApiGetPageInfo.bind(this)}]
+            ['Frontend.closePopup',       this._onApiClosePopup.bind(this)],
+            ['Frontend.copySelection',    this._onApiCopySelection.bind(this)],
+            ['Frontend.getSelectionText', this._onApiGetSelectionText.bind(this)],
+            ['Frontend.getPopupInfo',     this._onApiGetPopupInfo.bind(this)],
+            ['Frontend.getPageInfo',      this._onApiGetPageInfo.bind(this)]
         ]);
         /* eslint-enable no-multi-spaces */
 
diff --git a/ext/js/app/popup-factory.js b/ext/js/app/popup-factory.js
index 41984841..184a55ca 100644
--- a/ext/js/app/popup-factory.js
+++ b/ext/js/app/popup-factory.js
@@ -49,21 +49,21 @@ export class PopupFactory {
         this._frameOffsetForwarder.prepare();
         /* eslint-disable no-multi-spaces */
         yomitan.crossFrame.registerHandlers([
-            ['PopupFactory.getOrCreatePopup',     {async: true,  handler: this._onApiGetOrCreatePopup.bind(this)}],
-            ['PopupFactory.setOptionsContext',    {async: true,  handler: this._onApiSetOptionsContext.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: 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)}]
+            ['PopupFactory.getOrCreatePopup',     this._onApiGetOrCreatePopup.bind(this)],
+            ['PopupFactory.setOptionsContext',    this._onApiSetOptionsContext.bind(this)],
+            ['PopupFactory.hide',                 this._onApiHide.bind(this)],
+            ['PopupFactory.isVisible',            this._onApiIsVisibleAsync.bind(this)],
+            ['PopupFactory.setVisibleOverride',   this._onApiSetVisibleOverride.bind(this)],
+            ['PopupFactory.clearVisibleOverride', this._onApiClearVisibleOverride.bind(this)],
+            ['PopupFactory.containsPoint',        this._onApiContainsPoint.bind(this)],
+            ['PopupFactory.showContent',          this._onApiShowContent.bind(this)],
+            ['PopupFactory.setCustomCss',         this._onApiSetCustomCss.bind(this)],
+            ['PopupFactory.clearAutoPlayTimer',   this._onApiClearAutoPlayTimer.bind(this)],
+            ['PopupFactory.setContentScale',      this._onApiSetContentScale.bind(this)],
+            ['PopupFactory.updateTheme',          this._onApiUpdateTheme.bind(this)],
+            ['PopupFactory.setCustomOuterCss',    this._onApiSetCustomOuterCss.bind(this)],
+            ['PopupFactory.getFrameSize',         this._onApiGetFrameSize.bind(this)],
+            ['PopupFactory.setFrameSize',         this._onApiSetFrameSize.bind(this)]
         ]);
         /* eslint-enable no-multi-spaces */
     }
diff --git a/ext/js/background/backend.js b/ext/js/background/backend.js
index 09edbd6e..c3de6fc7 100644
--- a/ext/js/background/backend.js
+++ b/ext/js/background/backend.js
@@ -149,51 +149,51 @@ export class Backend {
         this._permissionsUtil = new PermissionsUtil();
 
         /* eslint-disable no-multi-spaces */
-        /** @type {import('backend').MessageHandlerMap} */
-        this._messageHandlers = new Map(/** @type {import('backend').MessageHandlerMapInit} */ ([
-            ['requestBackendReadySignal',    {async: false, contentScript: true,  handler: this._onApiRequestBackendReadySignal.bind(this)}],
-            ['optionsGet',                   {async: false, contentScript: true,  handler: this._onApiOptionsGet.bind(this)}],
-            ['optionsGetFull',               {async: false, contentScript: true,  handler: this._onApiOptionsGetFull.bind(this)}],
-            ['kanjiFind',                    {async: true,  contentScript: true,  handler: this._onApiKanjiFind.bind(this)}],
-            ['termsFind',                    {async: true,  contentScript: true,  handler: this._onApiTermsFind.bind(this)}],
-            ['parseText',                    {async: true,  contentScript: true,  handler: this._onApiParseText.bind(this)}],
-            ['getAnkiConnectVersion',        {async: true,  contentScript: true,  handler: this._onApiGetAnkiConnectVersion.bind(this)}],
-            ['isAnkiConnected',              {async: true,  contentScript: true,  handler: this._onApiIsAnkiConnected.bind(this)}],
-            ['addAnkiNote',                  {async: true,  contentScript: true,  handler: this._onApiAddAnkiNote.bind(this)}],
-            ['getAnkiNoteInfo',              {async: true,  contentScript: true,  handler: this._onApiGetAnkiNoteInfo.bind(this)}],
-            ['injectAnkiNoteMedia',          {async: true,  contentScript: true,  handler: this._onApiInjectAnkiNoteMedia.bind(this)}],
-            ['noteView',                     {async: true,  contentScript: true,  handler: this._onApiNoteView.bind(this)}],
-            ['suspendAnkiCardsForNote',      {async: true,  contentScript: true,  handler: this._onApiSuspendAnkiCardsForNote.bind(this)}],
-            ['commandExec',                  {async: false, contentScript: true,  handler: this._onApiCommandExec.bind(this)}],
-            ['getTermAudioInfoList',         {async: true,  contentScript: true,  handler: this._onApiGetTermAudioInfoList.bind(this)}],
-            ['sendMessageToFrame',           {async: false, contentScript: true,  handler: this._onApiSendMessageToFrame.bind(this)}],
-            ['broadcastTab',                 {async: false, contentScript: true,  handler: this._onApiBroadcastTab.bind(this)}],
-            ['frameInformationGet',          {async: true,  contentScript: true,  handler: this._onApiFrameInformationGet.bind(this)}],
-            ['injectStylesheet',             {async: true,  contentScript: true,  handler: this._onApiInjectStylesheet.bind(this)}],
-            ['getStylesheetContent',         {async: true,  contentScript: true,  handler: this._onApiGetStylesheetContent.bind(this)}],
-            ['getEnvironmentInfo',           {async: false, contentScript: true,  handler: this._onApiGetEnvironmentInfo.bind(this)}],
-            ['clipboardGet',                 {async: true,  contentScript: true,  handler: this._onApiClipboardGet.bind(this)}],
-            ['getDisplayTemplatesHtml',      {async: true,  contentScript: true,  handler: this._onApiGetDisplayTemplatesHtml.bind(this)}],
-            ['getZoom',                      {async: true,  contentScript: true,  handler: this._onApiGetZoom.bind(this)}],
-            ['getDefaultAnkiFieldTemplates', {async: false, contentScript: true,  handler: this._onApiGetDefaultAnkiFieldTemplates.bind(this)}],
-            ['getDictionaryInfo',            {async: true,  contentScript: true,  handler: this._onApiGetDictionaryInfo.bind(this)}],
-            ['purgeDatabase',                {async: true,  contentScript: false, handler: this._onApiPurgeDatabase.bind(this)}],
-            ['getMedia',                     {async: true,  contentScript: true,  handler: this._onApiGetMedia.bind(this)}],
-            ['log',                          {async: false, contentScript: true,  handler: this._onApiLog.bind(this)}],
-            ['logIndicatorClear',            {async: false, contentScript: true,  handler: this._onApiLogIndicatorClear.bind(this)}],
-            ['createActionPort',             {async: false, contentScript: true,  handler: this._onApiCreateActionPort.bind(this)}],
-            ['modifySettings',               {async: true,  contentScript: true,  handler: this._onApiModifySettings.bind(this)}],
-            ['getSettings',                  {async: false, contentScript: true,  handler: this._onApiGetSettings.bind(this)}],
-            ['setAllSettings',               {async: true,  contentScript: false, handler: this._onApiSetAllSettings.bind(this)}],
-            ['getOrCreateSearchPopup',       {async: true,  contentScript: true,  handler: this._onApiGetOrCreateSearchPopup.bind(this)}],
-            ['isTabSearchPopup',             {async: true,  contentScript: true,  handler: this._onApiIsTabSearchPopup.bind(this)}],
-            ['triggerDatabaseUpdated',       {async: false, contentScript: true,  handler: this._onApiTriggerDatabaseUpdated.bind(this)}],
-            ['testMecab',                    {async: true,  contentScript: true,  handler: this._onApiTestMecab.bind(this)}],
-            ['textHasJapaneseCharacters',    {async: false, contentScript: true,  handler: this._onApiTextHasJapaneseCharacters.bind(this)}],
-            ['getTermFrequencies',           {async: true,  contentScript: true,  handler: this._onApiGetTermFrequencies.bind(this)}],
-            ['findAnkiNotes',                {async: true,  contentScript: true,  handler: this._onApiFindAnkiNotes.bind(this)}],
-            ['loadExtensionScripts',         {async: true,  contentScript: true,  handler: this._onApiLoadExtensionScripts.bind(this)}],
-            ['openCrossFramePort',           {async: false, contentScript: true,  handler: this._onApiOpenCrossFramePort.bind(this)}]
+        /** @type {import('core').MessageHandlerMap} */
+        this._messageHandlers = new Map(/** @type {import('core').MessageHandlerMapInit} */ ([
+            ['requestBackendReadySignal',    this._onApiRequestBackendReadySignal.bind(this)],
+            ['optionsGet',                   this._onApiOptionsGet.bind(this)],
+            ['optionsGetFull',               this._onApiOptionsGetFull.bind(this)],
+            ['kanjiFind',                    this._onApiKanjiFind.bind(this)],
+            ['termsFind',                    this._onApiTermsFind.bind(this)],
+            ['parseText',                    this._onApiParseText.bind(this)],
+            ['getAnkiConnectVersion',        this._onApiGetAnkiConnectVersion.bind(this)],
+            ['isAnkiConnected',              this._onApiIsAnkiConnected.bind(this)],
+            ['addAnkiNote',                  this._onApiAddAnkiNote.bind(this)],
+            ['getAnkiNoteInfo',              this._onApiGetAnkiNoteInfo.bind(this)],
+            ['injectAnkiNoteMedia',          this._onApiInjectAnkiNoteMedia.bind(this)],
+            ['noteView',                     this._onApiNoteView.bind(this)],
+            ['suspendAnkiCardsForNote',      this._onApiSuspendAnkiCardsForNote.bind(this)],
+            ['commandExec',                  this._onApiCommandExec.bind(this)],
+            ['getTermAudioInfoList',         this._onApiGetTermAudioInfoList.bind(this)],
+            ['sendMessageToFrame',           this._onApiSendMessageToFrame.bind(this)],
+            ['broadcastTab',                 this._onApiBroadcastTab.bind(this)],
+            ['frameInformationGet',          this._onApiFrameInformationGet.bind(this)],
+            ['injectStylesheet',             this._onApiInjectStylesheet.bind(this)],
+            ['getStylesheetContent',         this._onApiGetStylesheetContent.bind(this)],
+            ['getEnvironmentInfo',           this._onApiGetEnvironmentInfo.bind(this)],
+            ['clipboardGet',                 this._onApiClipboardGet.bind(this)],
+            ['getDisplayTemplatesHtml',      this._onApiGetDisplayTemplatesHtml.bind(this)],
+            ['getZoom',                      this._onApiGetZoom.bind(this)],
+            ['getDefaultAnkiFieldTemplates', this._onApiGetDefaultAnkiFieldTemplates.bind(this)],
+            ['getDictionaryInfo',            this._onApiGetDictionaryInfo.bind(this)],
+            ['purgeDatabase',                this._onApiPurgeDatabase.bind(this)],
+            ['getMedia',                     this._onApiGetMedia.bind(this)],
+            ['log',                          this._onApiLog.bind(this)],
+            ['logIndicatorClear',            this._onApiLogIndicatorClear.bind(this)],
+            ['createActionPort',             this._onApiCreateActionPort.bind(this)],
+            ['modifySettings',               this._onApiModifySettings.bind(this)],
+            ['getSettings',                  this._onApiGetSettings.bind(this)],
+            ['setAllSettings',               this._onApiSetAllSettings.bind(this)],
+            ['getOrCreateSearchPopup',       this._onApiGetOrCreateSearchPopup.bind(this)],
+            ['isTabSearchPopup',             this._onApiIsTabSearchPopup.bind(this)],
+            ['triggerDatabaseUpdated',       this._onApiTriggerDatabaseUpdated.bind(this)],
+            ['testMecab',                    this._onApiTestMecab.bind(this)],
+            ['textHasJapaneseCharacters',    this._onApiTextHasJapaneseCharacters.bind(this)],
+            ['getTermFrequencies',           this._onApiGetTermFrequencies.bind(this)],
+            ['findAnkiNotes',                this._onApiFindAnkiNotes.bind(this)],
+            ['loadExtensionScripts',         this._onApiLoadExtensionScripts.bind(this)],
+            ['openCrossFramePort',           this._onApiOpenCrossFramePort.bind(this)]
         ]));
         /* eslint-enable no-multi-spaces */
         /** @type {import('backend').MessageHandlerWithProgressMap} */
@@ -408,16 +408,6 @@ export class Backend {
     _onMessage({action, params}, sender, callback) {
         const messageHandler = this._messageHandlers.get(action);
         if (typeof messageHandler === 'undefined') { return false; }
-
-        if (!messageHandler.contentScript) {
-            try {
-                this._validatePrivilegedMessageSender(sender);
-            } catch (error) {
-                callback({error: ExtensionError.serialize(error)});
-                return false;
-            }
-        }
-
         return invokeMessageHandler(messageHandler, params, callback, sender);
     }
 
diff --git a/ext/js/background/offscreen.js b/ext/js/background/offscreen.js
index 85b6847b..bcbcda6b 100644
--- a/ext/js/background/offscreen.js
+++ b/ext/js/background/offscreen.js
@@ -52,23 +52,21 @@ export class Offscreen {
 
         /* eslint-disable no-multi-spaces */
         /** @type {import('offscreen').MessageHandlerMap} */
-        const messageHandlers = new Map([
-            ['clipboardGetTextOffscreen',    {async: true,  handler: this._getTextHandler.bind(this)}],
-            ['clipboardGetImageOffscreen',   {async: true,  handler: this._getImageHandler.bind(this)}],
-            ['clipboardSetBrowserOffscreen', {async: false, handler: this._setClipboardBrowser.bind(this)}],
-            ['databasePrepareOffscreen',     {async: true,  handler: this._prepareDatabaseHandler.bind(this)}],
-            ['getDictionaryInfoOffscreen',   {async: true,  handler: this._getDictionaryInfoHandler.bind(this)}],
-            ['databasePurgeOffscreen',       {async: true,  handler: this._purgeDatabaseHandler.bind(this)}],
-            ['databaseGetMediaOffscreen',    {async: true,  handler: this._getMediaHandler.bind(this)}],
-            ['translatorPrepareOffscreen',   {async: false, handler: this._prepareTranslatorHandler.bind(this)}],
-            ['findKanjiOffscreen',           {async: true,  handler: this._findKanjiHandler.bind(this)}],
-            ['findTermsOffscreen',           {async: true,  handler: this._findTermsHandler.bind(this)}],
-            ['getTermFrequenciesOffscreen',  {async: true,  handler: this._getTermFrequenciesHandler.bind(this)}],
-            ['clearDatabaseCachesOffscreen', {async: false, handler: this._clearDatabaseCachesHandler.bind(this)}]
-        ]);
+        this._messageHandlers = new Map(/** @type {import('offscreen').MessageHandlerMapInit} */ ([
+            ['clipboardGetTextOffscreen',    this._getTextHandler.bind(this)],
+            ['clipboardGetImageOffscreen',   this._getImageHandler.bind(this)],
+            ['clipboardSetBrowserOffscreen', this._setClipboardBrowser.bind(this)],
+            ['databasePrepareOffscreen',     this._prepareDatabaseHandler.bind(this)],
+            ['getDictionaryInfoOffscreen',   this._getDictionaryInfoHandler.bind(this)],
+            ['databasePurgeOffscreen',       this._purgeDatabaseHandler.bind(this)],
+            ['databaseGetMediaOffscreen',    this._getMediaHandler.bind(this)],
+            ['translatorPrepareOffscreen',   this._prepareTranslatorHandler.bind(this)],
+            ['findKanjiOffscreen',           this._findKanjiHandler.bind(this)],
+            ['findTermsOffscreen',           this._findTermsHandler.bind(this)],
+            ['getTermFrequenciesOffscreen',  this._getTermFrequenciesHandler.bind(this)],
+            ['clearDatabaseCachesOffscreen', this._clearDatabaseCachesHandler.bind(this)]
+        ]));
         /* eslint-enable no-multi-spaces */
-        /** @type {import('offscreen').MessageHandlerMap<string>} */
-        this._messageHandlers = messageHandlers;
 
         const onMessage = this._onMessage.bind(this);
         chrome.runtime.onMessage.addListener(onMessage);
@@ -172,7 +170,7 @@ export class Offscreen {
 
     /** @type {import('extension').ChromeRuntimeOnMessageCallback} */
     _onMessage({action, params}, sender, callback) {
-        const messageHandler = this._messageHandlers.get(action);
+        const messageHandler = this._messageHandlers.get(/** @type {import('offscreen').MessageType} */ (action));
         if (typeof messageHandler === 'undefined') { return false; }
         return invokeMessageHandler(messageHandler, params, callback, sender);
     }
diff --git a/ext/js/comm/cross-frame-api.js b/ext/js/comm/cross-frame-api.js
index 0d3f3275..023ca18e 100644
--- a/ext/js/comm/cross-frame-api.js
+++ b/ext/js/comm/cross-frame-api.js
@@ -351,7 +351,7 @@ export class CrossFrameAPI {
     }
 
     /**
-     * @param {import('core').MessageHandlerArray} messageHandlers
+     * @param {import('core').MessageHandlerMapInit} messageHandlers
      * @throws {Error}
      */
     registerHandlers(messageHandlers) {
diff --git a/ext/js/comm/frame-ancestry-handler.js b/ext/js/comm/frame-ancestry-handler.js
index b91046bc..261ea943 100644
--- a/ext/js/comm/frame-ancestry-handler.js
+++ b/ext/js/comm/frame-ancestry-handler.js
@@ -164,7 +164,9 @@ export class FrameAncestryHandler {
             };
 
             // Start
-            yomitan.crossFrame.registerHandlers([[responseMessageId, {async: false, handler: onMessage}]]);
+            yomitan.crossFrame.registerHandlers([
+                [responseMessageId, onMessage]
+            ]);
             resetTimeout();
             const frameId = this._frameId;
             this._requestFrameInfo(targetWindow, frameId, frameId, uniqueId, nonce);
diff --git a/ext/js/comm/frame-offset-forwarder.js b/ext/js/comm/frame-offset-forwarder.js
index af9bd268..afa6a5e6 100644
--- a/ext/js/comm/frame-offset-forwarder.js
+++ b/ext/js/comm/frame-offset-forwarder.js
@@ -36,7 +36,7 @@ export class FrameOffsetForwarder {
     prepare() {
         this._frameAncestryHandler.prepare();
         yomitan.crossFrame.registerHandlers([
-            ['FrameOffsetForwarder.getChildFrameRect', {async: false, handler: this._onMessageGetChildFrameRect.bind(this)}]
+            ['FrameOffsetForwarder.getChildFrameRect', this._onMessageGetChildFrameRect.bind(this)]
         ]);
     }
 
diff --git a/ext/js/core.js b/ext/js/core.js
index d2372352..9995ee5b 100644
--- a/ext/js/core.js
+++ b/ext/js/core.js
@@ -324,7 +324,7 @@ export function promiseAnimationFrame(timeout) {
  * Invokes a standard message handler. This function is used to react and respond
  * to communication messages within the extension.
  * @template {import('core').SafeAny} TParams
- * @param {import('core').MessageHandlerDetails} details Details about how to handle messages.
+ * @param {import('core').MessageHandler} handler The message handler function.
  * @param {TParams} params Information which was passed with the original message.
  * @param {(response: import('core').Response) => void} callback A callback function which is invoked after the handler has completed. The value passed
  *   to the function is in the format:
@@ -333,13 +333,10 @@ export function promiseAnimationFrame(timeout) {
  * @param {...*} extraArgs Additional arguments which are passed to the `handler` function.
  * @returns {boolean} `true` if the function is invoked asynchronously, `false` otherwise.
  */
-export function invokeMessageHandler({handler, async}, params, callback, ...extraArgs) {
+export function invokeMessageHandler(handler, params, callback, ...extraArgs) {
     try {
-        let promiseOrResult = handler(params, ...extraArgs);
-        if (async === 'dynamic') {
-            ({async, result: promiseOrResult} = promiseOrResult);
-        }
-        if (async) {
+        const promiseOrResult = handler(params, ...extraArgs);
+        if (promiseOrResult instanceof Promise) {
             /** @type {Promise<any>} */ (promiseOrResult).then(
                 (result) => { callback({result}); },
                 (error) => { callback({error: ExtensionError.serialize(error)}); }
diff --git a/ext/js/display/display-audio.js b/ext/js/display/display-audio.js
index 8cd1ccc3..30cf2b92 100644
--- a/ext/js/display/display-audio.js
+++ b/ext/js/display/display-audio.js
@@ -89,7 +89,7 @@ export class DisplayAudio {
             ['playAudioFromSource', this._onHotkeyActionPlayAudioFromSource.bind(this)]
         ]);
         this._display.registerDirectMessageHandlers([
-            ['Display.clearAutoPlayTimer', {async: false, handler: this._onMessageClearAutoPlayTimer.bind(this)}]
+            ['Display.clearAutoPlayTimer', this._onMessageClearAutoPlayTimer.bind(this)]
         ]);
         /* eslint-enable no-multi-spaces */
         this._display.on('optionsUpdated', this._onOptionsUpdated.bind(this));
diff --git a/ext/js/display/display.js b/ext/js/display/display.js
index d7b8f898..79cf79a8 100644
--- a/ext/js/display/display.js
+++ b/ext/js/display/display.js
@@ -207,15 +207,15 @@ export class Display extends EventDispatcher {
             ['previousEntryDifferentDictionary', () => { this._focusEntryWithDifferentDictionary(-1, true); }]
         ]);
         this.registerDirectMessageHandlers([
-            ['Display.setOptionsContext', {async: true,  handler: this._onMessageSetOptionsContext.bind(this)}],
-            ['Display.setContent',        {async: false, handler: this._onMessageSetContent.bind(this)}],
-            ['Display.setCustomCss',      {async: false, handler: this._onMessageSetCustomCss.bind(this)}],
-            ['Display.setContentScale',   {async: false, handler: this._onMessageSetContentScale.bind(this)}],
-            ['Display.configure',         {async: true,  handler: this._onMessageConfigure.bind(this)}],
-            ['Display.visibilityChanged', {async: false, handler: this._onMessageVisibilityChanged.bind(this)}]
+            ['Display.setOptionsContext', this._onMessageSetOptionsContext.bind(this)],
+            ['Display.setContent',        this._onMessageSetContent.bind(this)],
+            ['Display.setCustomCss',      this._onMessageSetCustomCss.bind(this)],
+            ['Display.setContentScale',   this._onMessageSetContentScale.bind(this)],
+            ['Display.configure',         this._onMessageConfigure.bind(this)],
+            ['Display.visibilityChanged', this._onMessageVisibilityChanged.bind(this)]
         ]);
         this.registerWindowMessageHandlers([
-            ['Display.extensionUnloaded', {async: false, handler: this._onMessageExtensionUnloaded.bind(this)}]
+            ['Display.extensionUnloaded', this._onMessageExtensionUnloaded.bind(this)]
         ]);
         /* eslint-enable no-multi-spaces */
     }
@@ -328,7 +328,7 @@ export class Display extends EventDispatcher {
         this._progressIndicatorVisible.on('change', this._onProgressIndicatorVisibleChanged.bind(this));
         yomitan.on('extensionUnloaded', this._onExtensionUnloaded.bind(this));
         yomitan.crossFrame.registerHandlers([
-            ['popupMessage', {async: 'dynamic', handler: this._onDirectMessage.bind(this)}]
+            ['popupMessage', this._onDirectMessage.bind(this)]
         ]);
         window.addEventListener('message', this._onWindowMessage.bind(this), false);
 
@@ -506,7 +506,7 @@ export class Display extends EventDispatcher {
     }
 
     /**
-     * @param {import('core').MessageHandlerArray} handlers
+     * @param {import('core').MessageHandlerMapInit} handlers
      */
     registerDirectMessageHandlers(handlers) {
         for (const [name, handlerInfo] of handlers) {
@@ -515,7 +515,7 @@ export class Display extends EventDispatcher {
     }
 
     /**
-     * @param {import('core').MessageHandlerArray} handlers
+     * @param {import('core').MessageHandlerMapInit} handlers
      */
     registerWindowMessageHandlers(handlers) {
         for (const [name, handlerInfo] of handlers) {
@@ -638,22 +638,17 @@ export class Display extends EventDispatcher {
 
     /**
      * @param {import('frame-client').Message<import('display').MessageDetails>} data
-     * @returns {import('core').MessageHandlerAsyncResult}
+     * @returns {import('core').MessageHandlerResult}
      * @throws {Error}
      */
     _onDirectMessage(data) {
         const {action, params} = this._authenticateMessageData(data);
-        const handlerInfo = this._directMessageHandlers.get(action);
-        if (typeof handlerInfo === 'undefined') {
+        const handler = this._directMessageHandlers.get(action);
+        if (typeof handler === 'undefined') {
             throw new Error(`Invalid action: ${action}`);
         }
 
-        const {async, handler} = handlerInfo;
-        const result = handler(params);
-        return {
-            async: typeof async === 'boolean' && async,
-            result
-        };
+        return handler(params);
     }
 
     /**
diff --git a/ext/js/display/search-display-controller.js b/ext/js/display/search-display-controller.js
index 44850cbb..4dd41736 100644
--- a/ext/js/display/search-display-controller.js
+++ b/ext/js/display/search-display-controller.js
@@ -96,9 +96,9 @@ export class SearchDisplayController {
         ]);
         /* eslint-disable no-multi-spaces */
         this._registerMessageHandlers([
-            ['SearchDisplayController.getMode',           {async: false, handler: this._onMessageGetMode.bind(this)}],
-            ['SearchDisplayController.setMode',           {async: false, handler: this._onMessageSetMode.bind(this)}],
-            ['SearchDisplayController.updateSearchQuery', {async: false, handler: this._onExternalSearchUpdate.bind(this)}]
+            ['SearchDisplayController.getMode',           this._onMessageGetMode.bind(this)],
+            ['SearchDisplayController.setMode',           this._onMessageSetMode.bind(this)],
+            ['SearchDisplayController.updateSearchQuery', this._onExternalSearchUpdate.bind(this)]
         ]);
         /* eslint-enable no-multi-spaces */
 
@@ -549,7 +549,7 @@ export class SearchDisplayController {
     }
 
     /**
-     * @param {import('core').MessageHandlerArray} handlers
+     * @param {import('core').MessageHandlerMapInit} handlers
      */
     _registerMessageHandlers(handlers) {
         for (const [name, handlerInfo] of handlers) {
diff --git a/ext/js/input/hotkey-handler.js b/ext/js/input/hotkey-handler.js
index f1512b8f..da763662 100644
--- a/ext/js/input/hotkey-handler.js
+++ b/ext/js/input/hotkey-handler.js
@@ -51,7 +51,7 @@ export class HotkeyHandler extends EventDispatcher {
         this._isPrepared = true;
         this._updateEventHandlers();
         yomitan.crossFrame.registerHandlers([
-            ['HotkeyHandler.forwardHotkey', {async: false, handler: this._onMessageForwardHotkey.bind(this)}]
+            ['HotkeyHandler.forwardHotkey', this._onMessageForwardHotkey.bind(this)]
         ]);
     }
 
diff --git a/ext/js/templates/sandbox/template-renderer-frame-api.js b/ext/js/templates/sandbox/template-renderer-frame-api.js
index 388401f2..56cedb97 100644
--- a/ext/js/templates/sandbox/template-renderer-frame-api.js
+++ b/ext/js/templates/sandbox/template-renderer-frame-api.js
@@ -27,10 +27,10 @@ export class TemplateRendererFrameApi {
         /** @type {import('./template-renderer.js').TemplateRenderer} */
         this._templateRenderer = templateRenderer;
         /** @type {import('core').MessageHandlerMap} */
-        this._windowMessageHandlers = new Map(/** @type {import('core').MessageHandlerArray} */ ([
-            ['render', {async: false, handler: this._onRender.bind(this)}],
-            ['renderMulti', {async: false, handler: this._onRenderMulti.bind(this)}],
-            ['getModifiedData', {async: false, handler: this._onGetModifiedData.bind(this)}]
+        this._windowMessageHandlers = new Map(/** @type {import('core').MessageHandlerMapInit} */ ([
+            ['render', this._onRender.bind(this)],
+            ['renderMulti', this._onRenderMulti.bind(this)],
+            ['getModifiedData', this._onGetModifiedData.bind(this)]
         ]));
     }
 
@@ -56,17 +56,17 @@ export class TemplateRendererFrameApi {
     }
 
     /**
-     * @param {import('core').MessageHandlerDetails} handlerItem
+     * @param {import('core').MessageHandler} handler
      * @param {string} action
      * @param {import('core').SerializableObject} params
      * @param {Window} source
      * @param {?string} id
      */
-    async _onWindowMessageInner({handler, async}, action, params, source, id) {
+    async _onWindowMessageInner(handler, action, params, source, id) {
         let response;
         try {
             let result = handler(params);
-            if (async) {
+            if (result instanceof Promise) {
                 result = await result;
             }
             response = {result};
diff --git a/ext/js/yomitan.js b/ext/js/yomitan.js
index 37455d00..1d6f7644 100644
--- a/ext/js/yomitan.js
+++ b/ext/js/yomitan.js
@@ -90,13 +90,13 @@ export class Yomitan extends EventDispatcher {
 
         /* eslint-disable no-multi-spaces */
         /** @type {import('core').MessageHandlerMap} */
-        this._messageHandlers = new Map(/** @type {import('core').MessageHandlerArray} */ ([
-            ['Yomitan.isReady',         {async: false, handler: this._onMessageIsReady.bind(this)}],
-            ['Yomitan.backendReady',    {async: false, handler: this._onMessageBackendReady.bind(this)}],
-            ['Yomitan.getUrl',          {async: false, handler: this._onMessageGetUrl.bind(this)}],
-            ['Yomitan.optionsUpdated',  {async: false, handler: this._onMessageOptionsUpdated.bind(this)}],
-            ['Yomitan.databaseUpdated', {async: false, handler: this._onMessageDatabaseUpdated.bind(this)}],
-            ['Yomitan.zoomChanged',     {async: false, handler: this._onMessageZoomChanged.bind(this)}]
+        this._messageHandlers = new Map(/** @type {import('core').MessageHandlerMapInit} */ ([
+            ['Yomitan.isReady',         this._onMessageIsReady.bind(this)],
+            ['Yomitan.backendReady',    this._onMessageBackendReady.bind(this)],
+            ['Yomitan.getUrl',          this._onMessageGetUrl.bind(this)],
+            ['Yomitan.optionsUpdated',  this._onMessageOptionsUpdated.bind(this)],
+            ['Yomitan.databaseUpdated', this._onMessageDatabaseUpdated.bind(this)],
+            ['Yomitan.zoomChanged',     this._onMessageZoomChanged.bind(this)]
         ]));
         /* eslint-enable no-multi-spaces */
     }