Faster loading of issue lists

Reduce page size to 10 when loading issues on GraphQL boards

app/assets/javascripts/boards/components/board_list.vue

 <script>
-import { GlLoadingIcon } from '@gitlab/ui';
+import { GlLoadingIcon, GlIntersectionObserver } from '@gitlab/ui';
 import Draggable from 'vuedraggable';
 import { mapActions, mapGetters, mapState } from 'vuex';
 import { sortableStart, sortableEnd } from '~/boards/mixins/sortable_default_options';
@@ -21,6 +21,7 @@ export default {
     BoardCard,
     BoardNewIssue,
     GlLoadingIcon,
+    GlIntersectionObserver,
   },
   props: {
     disabled: {
@@ -65,7 +66,7 @@ export default {
       return this.list.maxIssueCount > 0 && this.listItemsCount > this.list.maxIssueCount;
     },
     hasNextPage() {
-      return this.pageInfoByListId[this.list.id].hasNextPage;
+      return this.pageInfoByListId[this.list.id]?.hasNextPage;
     },
     loading() {
       return this.listsFlags[this.list.id]?.isLoading;
@@ -115,14 +116,9 @@ export default {
     eventHub.$on(`toggle-issue-form-${this.list.id}`, this.toggleForm);
     eventHub.$on(`scroll-board-list-${this.list.id}`, this.scrollToTop);
   },
-  mounted() {
-    // Scroll event on list to load more
-    this.listRef.addEventListener('scroll', this.onScroll);
-  },
   beforeDestroy() {
     eventHub.$off(`toggle-issue-form-${this.list.id}`, this.toggleForm);
     eventHub.$off(`scroll-board-list-${this.list.id}`, this.scrollToTop);
-    this.listRef.removeEventListener('scroll', this.onScroll);
   },
   methods: {
     ...mapActions(['fetchItemsForList', 'moveItem']),
@@ -144,16 +140,10 @@ export default {
     toggleForm() {
       this.showIssueForm = !this.showIssueForm;
     },
-    onScroll() {
-      window.requestAnimationFrame(() => {
-        if (
-          !this.loadingMore &&
-          this.scrollTop() > this.scrollHeight() - this.scrollOffset &&
-          this.hasNextPage
-        ) {
-          this.loadNextPage();
-        }
-      });
+    onReachingListBottom() {
+      if (!this.loadingMore && this.hasNextPage) {
+        this.loadNextPage();
+      }
     },
     handleDragOnStart() {
       sortableStart();
@@ -249,7 +239,9 @@ export default {
           data-testid="count-loading-icon"
         />
         <span v-if="showingAllItems">{{ showingAllItemsText }}</span>
-        <span v-else>{{ paginatedIssueText }}</span>
+        <gl-intersection-observer v-else @update="onReachingListBottom">
+          <span>{{ paginatedIssueText }}</span>
+        </gl-intersection-observer>
       </li>
     </component>
   </div>

app/assets/javascripts/boards/stores/actions.js

@@ -298,7 +298,7 @@ export default {
       filters: filterParams,
       isGroup: boardType === BoardType.group,
       isProject: boardType === BoardType.project,
-      first: 20,
+      first: 10,
       after: fetchNext ? state.pageInfoByListId[listId].endCursor : undefined,
     };
 

ee/app/assets/javascripts/boards/stores/actions.js

@@ -284,7 +284,7 @@ export default {
         ? { ...filterParams, epicWildcardId: EpicFilterType.none.toUpperCase() }
         : { ...filterParams, epicId },
       after: fetchNext ? state.pageInfoByListId[listId].endCursor : undefined,
-      first: forSwimlanes ? undefined : 20,
+      first: forSwimlanes ? undefined : 10,
     };
 
     if (getters.isEpicBoard) {

spec/frontend/boards/board_list_spec.js

@@ -181,12 +181,6 @@ describe('Board list component', () => {
       });
     });
 
-    it('loads more issues after scrolling', () => {
-      wrapper.vm.listRef.dispatchEvent(new Event('scroll'));
-
-      expect(actions.fetchItemsForList).toHaveBeenCalled();
-    });
-
     it('does not load issues if already loading', () => {
       wrapper = createComponent({
         state: { listsFlags: { 'gid://gitlab/List/1': { isLoadingMore: true } } },