1 files changed, 23 insertions, 0 deletions
diff --git a/app/assets/javascripts/lib/utils/sticky.js b/app/assets/javascripts/lib/utils/sticky.js
new file mode 100644
index 00000000000..43a808b6ab3
--- /dev/null
+++ b/app/assets/javascripts/lib/utils/sticky.js
@@ -0,0 +1,23 @@
+export const isSticky = (el, scrollY, stickyTop) => {
+  const top = el.offsetTop - scrollY;
+
+  if (top === stickyTop) {
+    el.classList.add('is-stuck');
+  } else {
+    el.classList.remove('is-stuck');
+  }
+};
+
+export default (el) => {
+  if (!el) return;
+
+  const computedStyle = window.getComputedStyle(el);
+
+  if (!/sticky/.test(computedStyle.position)) return;
+
+  const stickyTop = parseInt(computedStyle.top, 10);
+
+  document.addEventListener('scroll', () => isSticky(el, window.scrollY, stickyTop), {
+    passive: true,
+  });
+};