added Map.groupBy

src/main.ts

@@ -15,6 +15,7 @@ import '@fortawesome/fontawesome-free/css/all.css';
 import {createI18n} from '@/locale/locale';
 import 'vue3-toastify/dist/index.css';
 
+import './polyfill'
 
 const app = createApp(App);
 

src/polyfill.ts

@@ -0,0 +1,5 @@
+/// reference <../types/polyfill.d.ts>
+
+import groupBy from '@/util';
+
+Map.groupBy = groupBy;

src/util.ts

@@ -0,0 +1,11 @@
+export default function groupBy<K, V>(arr: V[], fn: (v: V) => K): Map<K, V[]> {
+  const map = new Map<K, V[]>();
+  arr.forEach(e => {
+    const key = fn(e);
+    if (!map.has(key)) {
+      map.set(key, [] as V[]);
+    }
+    map.get(key)!.push(e);
+  });
+  return map;
+}

types/polyfill.d.ts

@@ -0,0 +1,3 @@
+declare interface MapConstructor {
+  groupBy<K, V>(arr: V[], fn: (v: V) => K): Map<K, V[]>;
+}