Fix performance of sticky.js

Closes #39332

2 files changed, 3 insertions, 7 deletions

diff --git a/app/assets/javascripts/init_changes_dropdown.js b/app/assets/javascripts/init_changes_dropdown.js
index f785ed29e6c..e41f374b2e5 100644
--- a/app/assets/javascripts/init_changes_dropdown.js
+++ b/app/assets/javascripts/init_changes_dropdown.js
@@ -1,7 +1,7 @@
 import stickyMonitor from './lib/utils/sticky';
 
 export default () => {
-  stickyMonitor(document.querySelector('.js-diff-files-changed'));
+  stickyMonitor(document.querySelector('.js-diff-files-changed'), 76);
 
   $('.js-diff-stats-dropdown').glDropdown({
     filterable: true,
diff --git a/app/assets/javascripts/lib/utils/sticky.js b/app/assets/javascripts/lib/utils/sticky.js
index 64db42701ce..098afcfa1b4 100644
--- a/app/assets/javascripts/lib/utils/sticky.js
+++ b/app/assets/javascripts/lib/utils/sticky.js
@@ -28,14 +28,10 @@ export const isSticky = (el, scrollY, stickyTop, insertPlaceholder) => {
   }
 };
 
-export default (el, insertPlaceholder = true) => {
+export default (el, stickyTop, insertPlaceholder = true) => {
   if (!el) return;
 
-  const computedStyle = window.getComputedStyle(el);
-
-  if (!/sticky/.test(computedStyle.position)) return;
-
-  const stickyTop = parseInt(computedStyle.top, 10);
+  if (typeof CSS === 'undefined' || !(CSS.supports('(position: -webkit-sticky) or (position: sticky)'))) return;
 
   document.addEventListener('scroll', () => isSticky(el, window.scrollY, stickyTop, insertPlaceholder), {
     passive: true,