1 files changed, 44 insertions, 7 deletions

diff --git a/ext/mixed/js/core.js b/ext/mixed/js/core.js
index fd762e97..db7fc69b 100644
--- a/ext/mixed/js/core.js
+++ b/ext/mixed/js/core.js
@@ -278,11 +278,16 @@ const yomichan = (() => {
         constructor() {
             super();
 
-            this._isBackendPreparedResolve = null;
-            this._isBackendPreparedPromise = new Promise((resolve) => (this._isBackendPreparedResolve = resolve));
+            this._isBackendPreparedPromise = this.getTemporaryListenerResult(
+                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)]
@@ -312,6 +317,42 @@ const yomichan = (() => {
             this.trigger('orphaned', {error});
         }
 
+        getTemporaryListenerResult(eventHandler, userCallback, timeout=null) {
+            if (!(
+                typeof eventHandler.addListener === 'function' &&
+                typeof eventHandler.removeListener === 'function'
+            )) {
+                throw new Error('Event handler type not supported');
+            }
+
+            return new Promise((resolve, reject) => {
+                const runtimeMessageCallback = ({action, params}, sender, sendResponse) => {
+                    let timeoutId = null;
+                    if (timeout !== null) {
+                        timeoutId = window.setTimeout(() => {
+                            timeoutId = null;
+                            eventHandler.removeListener(runtimeMessageCallback);
+                            reject(new Error(`Listener timed out in ${timeout} ms`));
+                        }, timeout);
+                    }
+
+                    const cleanupResolve = (value) => {
+                        if (timeoutId !== null) {
+                            window.clearTimeout(timeoutId);
+                            timeoutId = null;
+                        }
+                        eventHandler.removeListener(runtimeMessageCallback);
+                        sendResponse();
+                        resolve(value);
+                    };
+
+                    userCallback({action, params}, {resolve: cleanupResolve, sender});
+                };
+
+                eventHandler.addListener(runtimeMessageCallback);
+            });
+        }
+
         // Private
 
         _onMessage({action, params}, sender, callback) {
@@ -323,10 +364,6 @@ const yomichan = (() => {
             return false;
         }
 
-        _onBackendPrepared() {
-            this._isBackendPreparedResolve();
-        }
-
         _onMessageGetUrl() {
             return {url: window.location.href};
         }