Revert "refactor: 可読性のため一部でArray.prototype.atを使うように" (#115)

* Revert "refactor: 可読性のため一部で`Array.prototype.at`を使うように (#11274)"

This reverts commit 2b6dbd4fcb.

* Apply suggestions from code review

---------

Co-authored-by: okayurisotto <okayurisotto@proton.me>

packages/frontend/src/components/MkPagination.vue

@@ -233,7 +233,7 @@ const fetchMore = async (): Promise<void> => {
 		...(props.pagination.offsetMode ? {
 			offset: offset.value,
 		} : {
-			untilId: Array.from(items.value.keys()).at(-1),
+			untilId: Array.from(items.value.keys())[items.value.size - 1],
 		}),
 	}).then(res => {
 		for (let i = 0; i < res.length; i++) {
@@ -297,7 +297,7 @@ const fetchMoreAhead = async (): Promise<void> => {
 		...(props.pagination.offsetMode ? {
 			offset: offset.value,
 		} : {
-			sinceId: Array.from(items.value.keys()).at(-1),
+			sinceId: Array.from(items.value.keys())[items.value.size - 1],
 		}),
 	}).then(res => {
 		if (res.length === 0) {