fix Backend prepare issues in settings

ext/bg/js/backend.js

@@ -39,6 +39,8 @@ class Backend {
             url: window.location.href
         };
 
+        this.isPrepared = false;
+
         this.clipboardPasteTarget = document.querySelector('#clipboard-paste-target');
 
         this.popupWindow = null;
@@ -108,6 +110,8 @@ class Backend {
         }
         chrome.runtime.onMessage.addListener(this.onMessage.bind(this));
 
+        this.isPrepared = true;
+
         const options = this.getOptions(this.optionsContext);
         if (options.general.showGuide) {
             chrome.tabs.create({url: chrome.runtime.getURL('/bg/guide.html')});

ext/bg/js/settings/backup.js

@@ -362,10 +362,10 @@ async function _onSettingsResetConfirmClick() {
 
 // Setup
 
-window.addEventListener('DOMContentLoaded', () => {
+function backupInitialize() {
     document.querySelector('#settings-export').addEventListener('click', _onSettingsExportClick, false);
     document.querySelector('#settings-import').addEventListener('click', _onSettingsImportClick, false);
     document.querySelector('#settings-import-file').addEventListener('change', _onSettingsImportFileChange, false);
     document.querySelector('#settings-reset').addEventListener('click', _onSettingsResetClick, false);
     document.querySelector('#settings-reset-modal-confirm').addEventListener('click', _onSettingsResetConfirmClick, false);
-}, false);
+}

ext/bg/js/settings/main.js

@@ -21,7 +21,7 @@ utilBackend, utilIsolate, utilBackgroundIsolate
 ankiErrorShown, ankiFieldsToDict
 ankiTemplatesUpdateValue, onAnkiOptionsChanged, onDictionaryOptionsChanged
 appearanceInitialize, audioSettingsInitialize, profileOptionsSetup, dictSettingsInitialize
-ankiInitialize, ankiTemplatesInitialize, storageInfoInitialize
+ankiInitialize, ankiTemplatesInitialize, storageInfoInitialize, backupInitialize
 */
 
 function getOptionsMutable(optionsContext) {
@@ -262,6 +262,8 @@ function showExtensionInformation() {
 
 
 async function onReady() {
+    await yomichan.prepare();
+
     showExtensionInformation();
 
     formSetupEventListeners();
@@ -271,6 +273,7 @@ async function onReady() {
     await dictSettingsInitialize();
     ankiInitialize();
     ankiTemplatesInitialize();
+    backupInitialize();
 
     storageInfoInitialize();
 

ext/bg/js/util.js

@@ -73,7 +73,11 @@ function utilStringHashCode(string) {
 }
 
 function utilBackend() {
-    return chrome.extension.getBackgroundPage().yomichanBackend;
+    const backend = chrome.extension.getBackgroundPage().yomichanBackend;
+    if (!backend.isPrepared) {
+        throw new Error('Backend not ready yet');
+    }
+    return backend;
 }
 
 async function utilAnkiGetModelNames() {