fixes for sidebar jumping

app/assets/javascripts/fly_out_nav.js

-import Cookies from 'js-cookie';
 import bp from './breakpoints';
 
 let headerHeight = 50;
+let sidebar;
+
+export const setSidebar = (el) => { sidebar = el; };
 
 export const getHeaderHeight = () => headerHeight;
 
 export const canShowActiveSubItems = (el) => {
-  const isHiddenByMedia = bp.getBreakpointSize() === 'sm' || bp.getBreakpointSize() === 'md';
-
-  if (el.classList.contains('active') && !isHiddenByMedia) {
-    return Cookies.get('sidebar_collapsed') === 'true';
+  if (el.classList.contains('active') && (sidebar && !sidebar.classList.contains('sidebar-icons-only'))) {
+    return false;
   }
 
   return true;
@@ -61,10 +61,14 @@ export default () => {
   const items = [...document.querySelectorAll('.sidebar-top-level-items > li')]
     .filter(el => el.querySelector('.sidebar-sub-level-items'));
 
-  headerHeight = document.querySelector('.nav-sidebar').offsetTop;
+  sidebar = document.querySelector('.nav-sidebar');
 
-  items.forEach((el) => {
-    el.addEventListener('mouseenter', e => showSubLevelItems(e.currentTarget));
-    el.addEventListener('mouseleave', e => hideSubLevelItems(e.currentTarget));
-  });
+  if (sidebar) {
+    headerHeight = sidebar.offsetTop;
+
+    items.forEach((el) => {
+      el.addEventListener('mouseenter', e => showSubLevelItems(e.currentTarget));
+      el.addEventListener('mouseleave', e => hideSubLevelItems(e.currentTarget));
+    });
+  }
 };

spec/javascripts/fly_out_nav_spec.js

-import Cookies from 'js-cookie';
 import {
   calculateTop,
   hideSubLevelItems,
@@ -6,6 +5,7 @@ import {
   canShowSubItems,
   canShowActiveSubItems,
   getHeaderHeight,
+  setSidebar,
 } from '~/fly_out_nav';
 import bp from '~/breakpoints';
 
@@ -183,7 +183,7 @@ describe('Fly out sidebar navigation', () => {
 
   describe('canShowActiveSubItems', () => {
     afterEach(() => {
-      Cookies.remove('sidebar_collapsed');
+      setSidebar(null);
     });
 
     it('returns true by default', () => {
@@ -192,36 +192,23 @@ describe('Fly out sidebar navigation', () => {
       ).toBeTruthy();
     });
 
-    it('returns false when cookie is false & element is active', () => {
-      Cookies.set('sidebar_collapsed', 'false');
+    it('returns false when active & expanded sidebar', () => {
+      const sidebar = document.createElement('div');
       el.classList.add('active');
 
-      expect(
-        canShowActiveSubItems(el),
-      ).toBeFalsy();
-    });
-
-    it('returns true when cookie is false & element is active', () => {
-      Cookies.set('sidebar_collapsed', 'true');
-      el.classList.add('active');
+      setSidebar(sidebar);
 
       expect(
         canShowActiveSubItems(el),
-      ).toBeTruthy();
+      ).toBeFalsy();
     });
 
-    it('returns true when element is active & breakpoint is sm', () => {
-      breakpointSize = 'sm';
+    it('returns true when active & collapsed sidebar', () => {
+      const sidebar = document.createElement('div');
+      sidebar.classList.add('sidebar-icons-only');
       el.classList.add('active');
 
-      expect(
-        canShowActiveSubItems(el),
-      ).toBeTruthy();
-    });
-
-    it('returns true when element is active & breakpoint is md', () => {
-      breakpointSize = 'md';
-      el.classList.add('active');
+      setSidebar(sidebar);
 
       expect(
         canShowActiveSubItems(el),