perf: reduce iterations and allocations (#2481)

* Object.keys and Object.values were used in some for loops, which increased allocations and memory pressure unnecessarily.
* Implement the fastest possible emptyness check (`isEmpty` function) for checking if an object has any keys on it.

frontend/src/components/Playback/TrackList.vue

@@ -32,7 +32,7 @@
     <tbody>
       <template v-for="(tracksOnDisc, discNumber) in tracksPerDisc">
         <tr
-          v-if="Object.keys(tracksPerDisc).length > 1"
+          v-if="hasMultipleDiscs"
           :key="discNumber"
           class="disc-header">
           <td
@@ -125,6 +125,7 @@ import { useBaseItem } from '@/composables/apis';
 import { playbackManager } from '@/store/playback-manager';
 import { getItemDetailsLink } from '@/utils/items';
 import { formatTicks } from '@/utils/time';
+import { isEmpty } from '@/utils/validation';
 
 const { item } = defineProps<{
   item: BaseItemDto;
@@ -137,6 +138,7 @@ const { data: tracks } = await useBaseItem(getItemsApi, 'getItems')(() => ({
 }));
 
 const tracksPerDisc = computed(() => Object.groupBy(tracks.value, ({ ParentIndexNumber }) => ParentIndexNumber!));
+const hasMultipleDiscs = computed(() => !isEmpty(tracksPerDisc.value));
 
 /**
  * Check if a given BaseItemDto is playing

frontend/src/plugins/workers/generic/subtitles.ts

@@ -35,12 +35,12 @@ function replaceTags(input: string, tagMap: TagMap) {
   let formattedText = input;
 
   // Iterate through tag mappings
-  for (const [htmlTag, markdownTag] of Object.entries(tagMap)) {
+  for (const htmlTag in tagMap) {
     const escapedHtmlTag = htmlTag.replaceAll('\\', '\\\\');
     const regex = new RegExp(escapedHtmlTag, 'gi');
 
     formattedText = formattedText.replace(regex, (_, p1: string) => {
-      return markdownTag.replace('$1', p1.trim());
+      return tagMap[htmlTag].replace('$1', p1.trim());
     });
   }
 

frontend/src/store/playback-manager.ts

@@ -1133,12 +1133,12 @@ class PlaybackManagerStore extends CommonStore<PlaybackManagerState> {
             }
           };
 
-          for (const [action, handler] of Object.entries(actionHandlers)) {
+          for (const action in actionHandlers) {
             try {
               window.navigator.mediaSession.setActionHandler(
                 action as MediaSessionAction,
                 /* eslint-disable-next-line unicorn/no-null */
-                add ? handler : null
+                add ? actionHandlers[action as keyof typeof actionHandlers] ?? null : null
               );
             } catch {
               console.error(

frontend/src/utils/validation.ts

@@ -63,6 +63,17 @@ export function isObj(value: unknown): value is object {
   return typeof value === 'object' && !isNull(value);
 }
 
+/**
+ * Check if an object is empty
+ */
+export function isEmpty(value: object): boolean {
+  for (const _ in value) {
+    return false;
+  }
+
+  return true;
+}
+
 /**
  * TypeScript type guard for AxiosError
  */