use getTemporaryListenerResult in other places

ext/fg/js/popup.js

@@ -203,12 +203,22 @@ class Popup {
             this._messageToken = await apiGetMessageToken();
         }
 
-        return new Promise((resolve) => {
+        const popupPreparedPromise = yomichan.getTemporaryListenerResult(
+            chrome.runtime.onMessage,
+            ({action, params}, {resolve}) => {
+                if (
+                    action === 'popupPrepareCompleted' &&
+                    isObject(params) &&
+                    params.targetPopupId === this._id
+                ) {
+                    resolve();
+                }
+            }
+        );
+
         const parentFrameId = (typeof this._frameId === 'number' ? this._frameId : null);
         this._container.setAttribute('src', chrome.runtime.getURL('/fg/float.html'));
         this._container.addEventListener('load', () => {
-                this._listenForDisplayPrepareCompleted(resolve);
-
             this._invokeApi('prepare', {
                 popupInfo: {
                     id: this._id,
@@ -223,7 +233,8 @@ class Popup {
         this._observeFullscreen(true);
         this._onFullscreenChanged();
         this._injectStyles();
-        });
+
+        return popupPreparedPromise;
     }
 
     async _injectStyles() {
@@ -358,21 +369,6 @@ class Popup {
         contentWindow.postMessage({action, params, token}, this._targetOrigin);
     }
 
-    _listenForDisplayPrepareCompleted(resolve) {
-        const runtimeMessageCallback = ({action, params}, sender, callback) => {
-            if (
-                action === 'popupPrepareCompleted' &&
-                isObject(params) &&
-                params.targetPopupId === this._id
-            ) {
-                chrome.runtime.onMessage.removeListener(runtimeMessageCallback);
-                callback();
-                resolve();
-            }
-        };
-        chrome.runtime.onMessage.addListener(runtimeMessageCallback);
-    }
-
     static _getFullscreenElement() {
         return (
             document.fullscreenElement ||

ext/mixed/js/core.js

@@ -278,11 +278,16 @@ const yomichan = (() => {
         constructor() {
             super();
 
-            this._isBackendPreparedResolve = null;
+            this._isBackendPreparedPromise = this.getTemporaryListenerResult(
-            this._isBackendPreparedPromise = new Promise((resolve) => (this._isBackendPreparedResolve = resolve));
+                chrome.runtime.onMessage,
+                ({action}, {resolve}) => {
+                    if (action === 'backendPrepared') {
+                        resolve();
+                    }
+                }
+            );
 
             this._messageHandlers = new Map([
-                ['backendPrepared', this._onBackendPrepared.bind(this)],
                 ['getUrl', this._onMessageGetUrl.bind(this)],
                 ['optionsUpdated', this._onMessageOptionsUpdated.bind(this)],
                 ['zoomChanged', this._onMessageZoomChanged.bind(this)]
@@ -362,10 +367,6 @@ const yomichan = (() => {
             return false;
         }
 
-        _onBackendPrepared() {
-            this._isBackendPreparedResolve();
-        }
-
         _onMessageGetUrl() {
             return {url: window.location.href};
         }