Merge branch 'tz-preload-mr-list' into 'master'

Prefetches Issue, MR and ToDo Lists

See merge request gitlab-org/gitlab!76540

app/assets/javascripts/lib/utils/navigation_utility.js

@@ -13,3 +13,42 @@ export default function findAndFollowLink(selector) {
     visitUrl(link);
   }
 }
+
+export function prefetchDocument(url) {
+  const newPrefetchLink = document.createElement('link');
+  newPrefetchLink.rel = 'prefetch';
+  newPrefetchLink.href = url;
+  newPrefetchLink.setAttribute('as', 'document');
+  document.head.appendChild(newPrefetchLink);
+}
+
+export function initPrefetchLinks(selector) {
+  document.querySelectorAll(selector).forEach((el) => {
+    let mouseOverTimer;
+
+    const mouseOutHandler = () => {
+      if (mouseOverTimer) {
+        clearTimeout(mouseOverTimer);
+        mouseOverTimer = undefined;
+      }
+    };
+
+    const mouseOverHandler = () => {
+      el.addEventListener('mouseout', mouseOutHandler, { once: true, passive: true });
+
+      mouseOverTimer = setTimeout(() => {
+        if (el.href) prefetchDocument(el.href);
+
+        // Only execute once
+        el.removeEventListener('mouseover', mouseOverHandler, true);
+
+        mouseOverTimer = undefined;
+      }, 100);
+    };
+
+    el.addEventListener('mouseover', mouseOverHandler, {
+      capture: true,
+      passive: true,
+    });
+  });
+}

app/assets/javascripts/main.js

@@ -14,6 +14,7 @@ import { GlBreakpointInstance as bp } from '@gitlab/ui/dist/utils';
 import { initRails } from '~/lib/utils/rails_ujs';
 import * as popovers from '~/popovers';
 import * as tooltips from '~/tooltips';
+import { initPrefetchLinks } from '~/lib/utils/navigation_utility';
 import initAlertHandler from './alert_handler';
 import { addDismissFlashClickListener } from './flash';
 import initTodoToggle from './header';
@@ -90,6 +91,7 @@ function deferredInitialisation() {
   initTopNav();
   initBreadcrumbs();
   initTodoToggle();
+  initPrefetchLinks('.js-prefetch-document');
   initLogoAnimation();
   initServicePingConsent();
   initUserPopovers();

app/views/layouts/header/_default.html.haml

@@ -46,7 +46,7 @@
                 = sprite_icon(search_menu_item.fetch(:icon))
           - if header_link?(:issues)
             = nav_link(path: 'dashboard#issues', html_options: { class: "user-counter" }) do
-              = link_to assigned_issues_dashboard_path, title: _('Issues'), class: 'dashboard-shortcuts-issues', aria: { label: _('Issues') },
+              = link_to assigned_issues_dashboard_path, title: _('Issues'), class: 'dashboard-shortcuts-issues js-prefetch-document', aria: { label: _('Issues') },
                 data: { qa_selector: 'issues_shortcut_button', toggle: 'tooltip', placement: 'bottom',
                 track_label: 'main_navigation',
                 track_action: 'click_issues_link',
@@ -75,18 +75,18 @@
                   %li.dropdown-header
                     = _('Merge requests')
                   %li
-                    = link_to assigned_mrs_dashboard_path, class: 'gl-display-flex! gl-align-items-center' do
+                    = link_to assigned_mrs_dashboard_path, class: 'gl-display-flex! gl-align-items-center js-prefetch-document' do
                       = _('Assigned to you')
                       %span.badge.gl-badge.badge-pill.badge-muted.merge-request-badge.gl-ml-auto.js-assigned-mr-count{ class: "" }
                         = user_merge_requests_counts[:assigned]
                   %li
-                    = link_to reviewer_mrs_dashboard_path, class: 'gl-display-flex! gl-align-items-center' do
+                    = link_to reviewer_mrs_dashboard_path, class: 'gl-display-flex! gl-align-items-center js-prefetch-document' do
                       = _('Review requests for you')
                       %span.badge.gl-badge.badge-pill.badge-muted.merge-request-badge.gl-ml-auto.js-reviewer-mr-count{ class: "" }
                         = user_merge_requests_counts[:review_requested]
           - if header_link?(:todos)
             = nav_link(controller: 'dashboard/todos', html_options: { class: "user-counter" }) do
-              = link_to dashboard_todos_path, title: _('To-Do List'), aria: { label: _('To-Do List') }, class: 'shortcuts-todos',
+              = link_to dashboard_todos_path, title: _('To-Do List'), aria: { label: _('To-Do List') }, class: 'shortcuts-todos js-prefetch-document',
                 data: { qa_selector: 'todos_shortcut_button', toggle: 'tooltip', placement: 'bottom',
                 track_label: 'main_navigation',
                 track_action: 'click_to_do_link',

app/views/projects/merge_requests/_merge_request.html.haml

@@ -9,7 +9,7 @@
     .issuable-main-info
       .merge-request-title.title
         %span.merge-request-title-text.js-onboarding-mr-item
-          = link_to merge_request.title, merge_request_path(merge_request)
+          = link_to merge_request.title, merge_request_path(merge_request), class: 'js-prefetch-document'
         - if merge_request.tasks?
           %span.task-status.d-none.d-sm-inline-block
              

spec/frontend/lib/utils/navigation_utility_spec.js

 import findAndFollowLink from '~/lib/utils/navigation_utility';
+import * as navigationUtils from '~/lib/utils/navigation_utility';
 import { visitUrl } from '~/lib/utils/url_utility';
 
 jest.mock('~/lib/utils/url_utility');
@@ -21,3 +22,91 @@ describe('findAndFollowLink', () => {
     expect(visitUrl).not.toHaveBeenCalled();
   });
 });
+
+describe('prefetchDocument', () => {
+  it('creates a prefetch link tag', () => {
+    const linkElement = document.createElement('link');
+
+    jest.spyOn(document, 'createElement').mockImplementation(() => linkElement);
+    jest.spyOn(document.head, 'appendChild');
+
+    navigationUtils.prefetchDocument('index.htm');
+
+    expect(document.head.appendChild).toHaveBeenCalledWith(linkElement);
+    expect(linkElement.href).toEqual('http://test.host/index.htm');
+    expect(linkElement.rel).toEqual('prefetch');
+    expect(linkElement.getAttribute('as')).toEqual('document');
+  });
+});
+
+describe('initPrefetchLinks', () => {
+  let newLink;
+
+  beforeEach(() => {
+    newLink = document.createElement('a');
+    newLink.href = 'index_prefetch.htm';
+    newLink.classList.add('js-test-prefetch-link');
+    document.body.appendChild(newLink);
+  });
+
+  it('adds to all links mouse out handlers when hovered', () => {
+    const mouseOverEvent = new Event('mouseover');
+
+    jest.spyOn(newLink, 'addEventListener');
+
+    navigationUtils.initPrefetchLinks('.js-test-prefetch-link');
+    newLink.dispatchEvent(mouseOverEvent);
+
+    expect(newLink.addEventListener).toHaveBeenCalled();
+  });
+
+  it('it is not fired when less then 100ms over link', () => {
+    const mouseOverEvent = new Event('mouseover');
+    const mouseOutEvent = new Event('mouseout');
+
+    jest.spyOn(newLink, 'addEventListener');
+    jest.spyOn(navigationUtils, 'prefetchDocument').mockImplementation(() => true);
+
+    navigationUtils.initPrefetchLinks('.js-test-prefetch-link');
+    newLink.dispatchEvent(mouseOverEvent);
+    newLink.dispatchEvent(mouseOutEvent);
+
+    expect(navigationUtils.prefetchDocument).not.toHaveBeenCalled();
+  });
+
+  describe('executes correctly when hovering long enough', () => {
+    const mouseOverEvent = new Event('mouseover');
+
+    beforeEach(() => {
+      jest.useFakeTimers();
+
+      jest.spyOn(global, 'setTimeout');
+      jest.spyOn(newLink, 'removeEventListener');
+    });
+
+    it('calls prefetchDocument which adds to document', () => {
+      jest.spyOn(document.head, 'appendChild');
+
+      navigationUtils.initPrefetchLinks('.js-test-prefetch-link');
+      newLink.dispatchEvent(mouseOverEvent);
+
+      jest.runAllTimers();
+
+      expect(setTimeout).toHaveBeenCalledWith(expect.any(Function), 100);
+      expect(document.head.appendChild).toHaveBeenCalled();
+    });
+
+    it('removes Event Listener when fired so only done once', () => {
+      navigationUtils.initPrefetchLinks('.js-test-prefetch-link');
+      newLink.dispatchEvent(mouseOverEvent);
+
+      jest.runAllTimers();
+
+      expect(newLink.removeEventListener).toHaveBeenCalledWith(
+        'mouseover',
+        expect.any(Function),
+        true,
+      );
+    });
+  });
+});