diff --git a/src/addons/mod/forum/components/index/index.ts b/src/addons/mod/forum/components/index/index.ts
index a9c6fc7e8..33c844ddf 100644
--- a/src/addons/mod/forum/components/index/index.ts
+++ b/src/addons/mod/forum/components/index/index.ts
@@ -48,7 +48,6 @@ import { CoreSplitViewComponent } from '@components/split-view/split-view';
 import { AddonModForumDiscussionOptionsMenuComponent } from '../discussion-options-menu/discussion-options-menu';
 import { AddonModForumSortOrderSelectorComponent } from '../sort-order-selector/sort-order-selector';
 import { CoreScreen } from '@services/screen';
-import { CoreArray } from '@singletons/array';
 import { AddonModForumPrefetchHandler } from '../../services/handlers/prefetch';
 import { AddonModForumModuleHandlerService } from '../../services/handlers/module';
 import { CoreRatingProvider } from '@features/rating/services/rating';
@@ -561,7 +560,7 @@ export class AddonModForumIndexComponent extends CoreCourseModuleMainActivityCom
                         }
 
                         if (this.discussions?.getSource().isOnlineDiscussion(disc)) {
-                            return CoreArray.contains(newDiscussionData.discussionIds ?? [], disc.discussion);
+                            return (newDiscussionData.discussionIds ?? []).includes(disc.discussion);
                         }
 
                         return false;
diff --git a/src/addons/mod/forum/services/forum-sync.ts b/src/addons/mod/forum/services/forum-sync.ts
index f033e9d22..f522dc34f 100644
--- a/src/addons/mod/forum/services/forum-sync.ts
+++ b/src/addons/mod/forum/services/forum-sync.ts
@@ -24,7 +24,6 @@ import { CoreSites } from '@services/sites';
 import { CoreSync } from '@services/sync';
 import { CoreUtils } from '@services/utils/utils';
 import { makeSingleton, Translate } from '@singletons';
-import { CoreArray } from '@singletons/array';
 import { CoreEvents } from '@singletons/events';
 import {
     AddonModForum,
@@ -90,7 +89,7 @@ export class AddonModForumSyncProvider extends CoreCourseActivitySyncBaseProvide
             // Do not sync same forum twice.
             const syncedForumIds: number[] = [];
             const promises = discussions.map(async discussion => {
-                if (CoreArray.contains(syncedForumIds, discussion.forumid)) {
+                if (syncedForumIds.includes(discussion.forumid)) {
                     return;
                 }
 
@@ -123,7 +122,7 @@ export class AddonModForumSyncProvider extends CoreCourseActivitySyncBaseProvide
             // Do not sync same discussion twice.
             const syncedDiscussionIds: number[] = [];
             const promises = replies.map(async reply => {
-                if (CoreArray.contains(syncedDiscussionIds, reply.discussionid)) {
+                if (syncedDiscussionIds.includes(reply.discussionid)) {
                     return;
                 }
 
diff --git a/src/addons/storagemanager/pages/courses-storage/courses-storage.ts b/src/addons/storagemanager/pages/courses-storage/courses-storage.ts
index 0f2e8a215..6a459959d 100644
--- a/src/addons/storagemanager/pages/courses-storage/courses-storage.ts
+++ b/src/addons/storagemanager/pages/courses-storage/courses-storage.ts
@@ -126,7 +126,7 @@ export class AddonStorageManagerCoursesStoragePage implements OnInit, OnDestroy
         try {
             await Promise.all(deletedCourseIds.map((courseId) => CoreCourseHelper.deleteCourseFiles(courseId)));
 
-            this.setDownloadedCourses(this.downloadedCourses.filter((course) => !CoreArray.contains(deletedCourseIds, course.id)));
+            this.setDownloadedCourses(this.downloadedCourses.filter((course) => !deletedCourseIds.includes(course.id)));
         } catch (error) {
             CoreDomUtils.showErrorModalDefault(error, Translate.instant('core.errordeletefile'));
         } finally {
diff --git a/src/core/services/ws.ts b/src/core/services/ws.ts
index 9d9e270de..38eb55151 100644
--- a/src/core/services/ws.ts
+++ b/src/core/services/ws.ts
@@ -31,7 +31,6 @@ import { CoreConstants } from '@/core/constants';
 import { CoreError } from '@classes/errors/error';
 import { CoreInterceptor } from '@classes/interceptor';
 import { makeSingleton, Translate, FileTransfer, Http, NativeHttp } from '@singletons';
-import { CoreArray } from '@singletons/array';
 import { CoreLogger } from '@singletons/logger';
 import { CoreWSError } from '@classes/errors/wserror';
 import { CoreAjaxError } from '@classes/errors/ajaxerror';
@@ -282,7 +281,7 @@ export class CoreWSProvider {
                 extension = CoreMimetypeUtils.getFileExtension(path) || '';
 
                 // Google Drive extensions will be considered invalid since Moodle usually converts them.
-                if (!extension || CoreArray.contains(['gdoc', 'gsheet', 'gslides', 'gdraw', 'php'], extension)) {
+                if (!extension || ['gdoc', 'gsheet', 'gslides', 'gdraw', 'php'].includes(extension)) {
                     // Not valid, get the file's mimetype.
                     const mimetype = await this.getRemoteFileMimeType(url);
 
diff --git a/src/core/singletons/array.ts b/src/core/singletons/array.ts
index 03a6ad4d3..5ed86de9b 100644
--- a/src/core/singletons/array.ts
+++ b/src/core/singletons/array.ts
@@ -23,8 +23,12 @@ export class CoreArray {
      * @param arr Array.
      * @param item Item.
      * @return Whether item is within the array.
+     * @deprecated since 4.1. Use arr.includes() instead.
      */
     static contains<T>(arr: T[], item: T): boolean {
+        // eslint-disable-next-line no-console
+        console.warn('CoreArray.contains is deprecated and will be removed soon. Please use array \'includes\' instead.');
+
         return arr.indexOf(item) !== -1;
     }