workaround by using .mjs

src/main/resources/web/index.html

@@ -169,6 +169,6 @@ script-src 'self' https://*.cloudflare.com/ https://alcdn.msauth.net/ https://*.
 <script src="https://alcdn.msauth.net/browser/2.15.0/js/msal-browser.min.js" integrity="sha384-/weuqUPkC0P9JxnstihEV1GHdWrheU9Qo3MbdTuxxKJM8l/cSTE5zGP5VBIM4TZN"
     crossorigin="anonymous"></script>
 
-<script type="module" src="js/page.js"></script>
+<script type="module" src="js/page.mjs"></script>
 </body>
 </html>

src/main/resources/web/js/account_manager.mjs

@@ -1,6 +1,6 @@
-import {getCorsProxy} from "./cors_proxy.js";
-import {checkFetchSuccess, filterNot, isSuccess} from "./util.js";
-import {addToast, refreshAccountList} from "./page.js";
+import {getCorsProxy} from "./cors_proxy.mjs";
+import {checkFetchSuccess, filterNot, isSuccess} from "./util.mjs";
+import {addToast, refreshAccountList} from "./page.mjs";
 
 let activeAccounts = [];
 
@@ -301,4 +301,4 @@ function getTokenPopup(username, request) {
             console.warn(error);
         }
     });
-}
+}

src/main/resources/web/js/cors_proxy.mjs

@@ -1,4 +1,4 @@
-import {refreshCorsStatus} from "./page.js";
+import {refreshCorsStatus} from "./page.mjs";
 
 function defaultCors() {
     return "https://crp123-cors.herokuapp.com/";

src/main/resources/web/js/page.mjs

@@ -1,6 +1,6 @@
 // Minecraft.id
-import {icanhazepoch, icanhazip} from "./util.js";
-import {getCorsProxy, setCorsProxy} from "./cors_proxy.js";
+import {icanhazepoch, icanhazip} from "./util.mjs";
+import {getCorsProxy, setCorsProxy} from "./cors_proxy.mjs";
 import {
     findAccountByMs,
     getActiveAccounts,
@@ -8,8 +8,8 @@ import {
     loginMc,
     loginMs, MicrosoftAccount,
     MojangAccount
-} from "./account_manager.js";
-import {connect, getWsUrl, removeToken, sendSocket, setWsUrl, unlisten} from "./websocket.js";
+} from "./account_manager.mjs";
+import {connect, getWsUrl, removeToken, sendSocket, setWsUrl, unlisten} from "./websocket.mjs";
 
 let mcIdUsername = null;
 let mcauth_code = null;
@@ -78,7 +78,7 @@ function swCacheFiles() {
         action: "cache",
         urls: performance.getEntriesByType("resource")
             .map(it => it.name)
-            .filter(it => it.endsWith(".js") || it.endsWith(".css") || it.endsWith(".png"))
+            .filter(it => it.endsWith(".mjs") || it.endsWith(".js") || it.endsWith(".css") || it.endsWith(".png"))
     })); // https://stackoverflow.com/questions/46830493/is-there-any-way-to-cache-all-files-of-defined-folder-path-in-service-worker
 }
 

src/main/resources/web/js/util.mjs

@@ -1,4 +1,4 @@
-import {getCorsProxy} from "./cors_proxy.js";
+import {getCorsProxy} from "./cors_proxy.mjs";
 
 export function isSuccess(status) {
     return status >= 200 && status < 300;
@@ -27,4 +27,4 @@ export function icanhazepoch() {
 
 export function filterNot(array, item) {
     return array.filter(it => it !== item);
-}
+}

src/main/resources/web/js/websocket.mjs

@@ -1,7 +1,7 @@
-import {authNotification} from "./notification.js";
-import {checkFetchSuccess} from "./util.js";
-import {findAccountByMcName} from "./account_manager.js";
-import {addListeningList, addToast, renderActions, resetHtml, setListenVisible, setWsStatus} from "./page.js";
+import {authNotification} from "./notification.mjs";
+import {checkFetchSuccess} from "./util.mjs";
+import {findAccountByMcName} from "./account_manager.mjs";
+import {addListeningList, addToast, renderActions, resetHtml, setListenVisible, setWsStatus} from "./page.mjs";
 
 let wsUrl = getWsUrl();
 let socket = null;
@@ -135,4 +135,4 @@ export function sendSocket(msg) {
         return
     }
     socket.send(msg);
-}
+}