add dropdown component

lib/utility/lgres.js

@@ -66,6 +66,7 @@ async function refreshLgres(template, lgres) {
     Object.defineProperty(lgres, 'r', {
         writable: false,
         configurable: false,
+        enumerable: false,
         value: function (key, defaultValue) {
             return getLanguage(this, key, defaultValue);
         }
@@ -76,16 +77,11 @@ async function refreshLgres(template, lgres) {
 
 function getLanguage(lgres, key, defaultValue) {
     let value = lgres[key];
-    if (value == null) {
-        value = defaultValue;
-    }
-    return value;
+    return value ?? defaultValue;
 }
 
 function applyLanguage(dom, result) {
-    if (dom == null) {
-        dom = document.body;
-    }
+    dom ??= document.body;
     for (let text of dom.querySelectorAll('[data-lgid]')) {
         const key = text.getAttribute('data-lgid');
         if (text.tagName === 'INPUT') {