diff --git a/frontend/src/components/manga/MangaListTable.vue b/frontend/src/components/manga/MangaListTable.vue
index 0870b45..2b26a8c 100644
--- a/frontend/src/components/manga/MangaListTable.vue
+++ b/frontend/src/components/manga/MangaListTable.vue
@@ -2,6 +2,7 @@
 import {Options, Vue} from 'vue-class-component';
 import {Prop, Watch} from 'vue-property-decorator';
 import {BTable, type TableItem} from 'bootstrap-vue-next';
+//@ts-ignore TS2307
 import type {TableFieldObject} from 'bootstrap-vue-next/dist/src/types';
 import type {ViewEntry, ViewList} from '@/components/manga/MangaList.vue';
 import MangaEntryDetailsModal from '@/components/manga/MangaEntryDetailsModal.vue';
@@ -110,7 +111,7 @@ export default class MangaListTable extends Vue {
   <div>
     <BTable ref="table" v-if="bTableRefreshHack" :fields="fields" :items="tableEntries" :primary-key="'id'"
             class="manga-table" hover striped responsive no-sort-reset sort-by="newChapters" sort-desc
-            @row-clicked="onRowClicked">
+            @row-clicked="onRowClicked as any /* TODO dumb typing issue */">
       <template #cell(media.coverImage.large)="data">
         <img :src="data.value as string" alt="cover-img" class="list-cover"/>
       </template>
diff --git a/frontend/src/components/manga/MangaLists.vue b/frontend/src/components/manga/MangaLists.vue
index 25ea64b..4a9ac70 100644
--- a/frontend/src/components/manga/MangaLists.vue
+++ b/frontend/src/components/manga/MangaLists.vue
@@ -7,6 +7,7 @@ import type {AniListMedia} from '@/data/models/anilist/AniListMedia';
 import type {MangaUpdatesRelation} from '@/data/models/mangaupdates/MangaUpdatesRelation';
 import type {MangaUpdatesSeries} from '@/data/models/mangaupdates/MangaUpdatesSeries';
 import type {MangaUpdatesChapter} from '@/data/models/mangaupdates/MangaUpdatesChapter';
+import groupBy from '@/util';
 
 @Options({
   name: 'MangaLists',
@@ -34,7 +35,7 @@ export default class MangaLists extends Vue {
 
   get chaptersBySeriesId(): Map<number, MangaUpdatesChapter[]> {
     const chapters = this.mangaStore.mangaUpdatesChapters;
-    return Map.groupBy(chapters, e => e.series_id);
+    return groupBy(chapters, e => e.series_id);
   }
 
   get viewLists(): ViewList[] {
diff --git a/frontend/src/data/api/AniListApi.ts b/frontend/src/data/api/AniListApi.ts
index 8f36fc4..8d5f07d 100644
--- a/frontend/src/data/api/AniListApi.ts
+++ b/frontend/src/data/api/AniListApi.ts
@@ -14,7 +14,7 @@ export default class AniListApi {
         'variables': {'name': userName},
       }),
     });
-    return (await handleJsonResponse(res)).data.User;
+    return ((await handleJsonResponse(res)) as any).data.User;
   }
 
   async fetchManga(userId: number): Promise<AniListMangaListCollection> {
@@ -28,6 +28,6 @@ export default class AniListApi {
         'variables': {'userId': userId, 'type': 'MANGA'},
       }),
     });
-    return (await handleJsonResponse(res)).data.MediaListCollection;
+    return ((await handleJsonResponse(res)) as any).data.MediaListCollection;
   }
 }
\ No newline at end of file
diff --git a/frontend/src/data/db/MangaUpdatesDb.ts b/frontend/src/data/db/MangaUpdatesDb.ts
index d697af9..eb6044e 100644
--- a/frontend/src/data/db/MangaUpdatesDb.ts
+++ b/frontend/src/data/db/MangaUpdatesDb.ts
@@ -1,6 +1,7 @@
 import {type IDBPDatabase, openDB} from 'idb';
 import type {MangaUpdatesSeries} from '@/data/models/mangaupdates/MangaUpdatesSeries';
 import type {MangaUpdatesChapter} from '@/data/models/mangaupdates/MangaUpdatesChapter';
+import type {MangaUpdatesRelation} from '@/data/models/mangaupdates/MangaUpdatesRelation';
 
 export type MuDb = IDBPDatabase<MangaUpdatesDBSchema>;
 
diff --git a/frontend/src/data/repository/mangaUpdates/MangaUpdatesRepository.ts b/frontend/src/data/repository/mangaUpdates/MangaUpdatesRepository.ts
index 0579021..b62e2df 100644
--- a/frontend/src/data/repository/mangaUpdates/MangaUpdatesRepository.ts
+++ b/frontend/src/data/repository/mangaUpdates/MangaUpdatesRepository.ts
@@ -1,6 +1,5 @@
 import MangaUpdatesDb from '@/data/db/MangaUpdatesDb';
 import type {MangaUpdatesRelation} from '@/data/models/mangaupdates/MangaUpdatesRelation';
-import type {MangaUpdatesMedia} from '@/data/models/mangaupdates/MangaUpdatesMedia';
 import type {MangaUpdatesChapter} from '@/data/models/mangaupdates/MangaUpdatesChapter';
 import type {MangaUpdatesSeries} from '@/data/models/mangaupdates/MangaUpdatesSeries';
 
@@ -25,7 +24,7 @@ export default class MangaUpdatesRepository {
 
   async getSeriesById(id: number) {
     return await MangaUpdatesDb.withDb(async db => {
-      return await db.get('series', id);
+      return await db.get('series', IDBKeyRange.only(id));
     });
   }
 
@@ -53,7 +52,7 @@ export default class MangaUpdatesRepository {
     });
   }
 
-  async updateSeries(newSeries: MangaUpdatesMedia[]) {
+  async updateSeries(newSeries: MangaUpdatesSeries[]) {
     return await MangaUpdatesDb.withDb(async db => {
       let txList = db.transaction('series', 'readwrite');
       await Promise.allSettled([
diff --git a/frontend/src/data/service/MangaUpdatesDataService.ts b/frontend/src/data/service/MangaUpdatesDataService.ts
index 841c546..fd38da4 100644
--- a/frontend/src/data/service/MangaUpdatesDataService.ts
+++ b/frontend/src/data/service/MangaUpdatesDataService.ts
@@ -5,6 +5,7 @@ import type {MangaUpdatesChapter} from '@/data/models/mangaupdates/MangaUpdatesC
 import type {MangaUpdatesSearchResultRecord} from '@/data/models/mangaupdates/MangaUpdatesSearchResultRecord';
 import stringSimilarity from 'string-similarity-js';
 import {ApiError} from '@/data/api/ApiUtils';
+import groupBy from '@/util';
 
 export default class MangaUpdatesDataService {
   private readonly mangaUpdatesApi = new MangaUpdatesApi();
@@ -63,7 +64,8 @@ export default class MangaUpdatesDataService {
           matching = results.results
             .filter(e => stringSimilarity(title, e.record.title, 2, false) >= 0.95)
             .filter(e => allowTypes.has(e.record.type.toLowerCase())) //check if a manga or similar but not novel
-            .filter(e => m.startDate.year - 1 <= e.record.year && e.record.year <= m.startDate.year + 1); //check year +-1
+            .filter(e => m.startDate.year - 1 <= parseInt('' + e.record.year)
+              && parseInt('' + e.record.year) <= m.startDate.year + 1); //check year +-1
           if (matching.length === 0) {
             continue;
           }
@@ -148,7 +150,7 @@ export default class MangaUpdatesDataService {
           .flat();
 
         //only keep chapter with the highest chapter number per group
-        const filtered = Array.from(Map.groupBy(updates, c => c.group).values())
+        const filtered = Array.from(groupBy(updates, c => c.group).values())
           .map(chaptersOfGroup => chaptersOfGroup.reduce((l, r) => l.chapter > r.chapter ? l : r, chaptersOfGroup[0]));
         await mangaStore.updateMangaUpdatesChapters(filtered);
       } finally {
diff --git a/frontend/src/locale/locale.ts b/frontend/src/locale/locale.ts
index d9ebd81..ea293c7 100644
--- a/frontend/src/locale/locale.ts
+++ b/frontend/src/locale/locale.ts
@@ -25,6 +25,7 @@ export function createI18n(): I18n {
     locale: browserLocale,
     fallbackLocale: 'en',
     messages: messages,
+    //@ts-ignore TS2769 TODO weird typing issue
     datetimeFormats: datetimeFormats,
     legacy: true,
   });
diff --git a/frontend/src/polyfill.ts b/frontend/src/polyfill.ts
deleted file mode 100644
index 0b9a076..0000000
--- a/frontend/src/polyfill.ts
+++ /dev/null
@@ -1,5 +0,0 @@
-/// reference <../types/polyfill.d.ts>
-
-import groupBy from '@/util';
-
-Map.groupBy = groupBy;
diff --git a/frontend/src/stores/MangaStore.ts b/frontend/src/stores/MangaStore.ts
index d9f0a21..6e2b213 100644
--- a/frontend/src/stores/MangaStore.ts
+++ b/frontend/src/stores/MangaStore.ts
@@ -7,6 +7,7 @@ import type {AniListMangaList} from '@/data/models/anilist/AniListMangaList';
 import type {MangaUpdatesRelation} from '@/data/models/mangaupdates/MangaUpdatesRelation';
 import type {MangaUpdatesChapter} from '@/data/models/mangaupdates/MangaUpdatesChapter';
 import type {MangaUpdatesSeries} from '@/data/models/mangaupdates/MangaUpdatesSeries';
+import groupBy from '@/util';
 
 @Store({
   id: 'MangaStore',
@@ -100,8 +101,8 @@ export class MangaStore extends Pinia {
     await this.dbStore.mangaUpdatesRepository.updateChapters(chapters);
 
     // update cache
-    const cachedById = Map.groupBy(this.cachedMangaUpdatesChapters, c => c.series_id);
-    const chaptersById = Map.groupBy(chapters, c => c.series_id);
+    const cachedById = groupBy(this.cachedMangaUpdatesChapters, c => c.series_id);
+    const chaptersById = groupBy(chapters, c => c.series_id);
     chaptersById.forEach((v, k) => cachedById.set(k, v));
     this.cachedMangaUpdatesChapters.splice(0);
     this.cachedMangaUpdatesChapters.push(...Array.from(cachedById.values()).flat());
diff --git a/frontend/types/polyfill.d.ts b/frontend/types/polyfill.d.ts
deleted file mode 100644
index 7a5eb7b..0000000
--- a/frontend/types/polyfill.d.ts
+++ /dev/null
@@ -1,3 +0,0 @@
-declare interface MapConstructor {
-  groupBy<K, V>(arr: V[], fn: (v: V) => K): Map<K, V[]>;
-}
\ No newline at end of file