Dynamically create offset for sticky bar

1 files changed, 25 insertions, 5 deletions

diff --git a/app/assets/javascripts/lib/utils/sticky.js b/app/assets/javascripts/lib/utils/sticky.js
index 283c0ec0410..f8f0a43f1cc 100644
--- a/app/assets/javascripts/lib/utils/sticky.js
+++ b/app/assets/javascripts/lib/utils/sticky.js
@@ -1,14 +1,34 @@
-export const isSticky = (el, scrollY, stickyTop) => {
+export const createPlaceholder = () => {
+  const placeholder = document.createElement('div');
+  placeholder.classList.add('sticky-placeholder');
+
+  return placeholder;
+};
+
+export const isSticky = (el, scrollY, stickyTop, insertPlaceholder) => {
   const top = Math.floor(el.offsetTop - scrollY);
 
-  if (top <= stickyTop) {
+  if (top <= stickyTop && !el.classList.contains('is-stuck')) {
+    const placeholder = insertPlaceholder ? createPlaceholder(el) : null;
+    const heightBefore = el.offsetHeight;
+
     el.classList.add('is-stuck');
-  } else {
+
+    if (insertPlaceholder) {
+      el.parentNode.insertBefore(placeholder, el.nextElementSibling);
+
+      placeholder.style.height = `${heightBefore - el.offsetHeight}px`;
+    }
+  } else if (top > stickyTop && el.classList.contains('is-stuck')) {
     el.classList.remove('is-stuck');
+
+    if (insertPlaceholder && el.nextElementSibling.classList.contains('sticky-placeholder')) {
+      el.nextElementSibling.remove();
+    }
   }
 };
 
-export default (el) => {
+export default (el, insertPlaceholder = true) => {
   if (!el) return;
 
   const computedStyle = window.getComputedStyle(el);
@@ -17,7 +37,7 @@ export default (el) => {
 
   const stickyTop = parseInt(computedStyle.top, 10);
 
-  document.addEventListener('scroll', () => isSticky(el, window.scrollY, stickyTop), {
+  document.addEventListener('scroll', () => isSticky(el, window.scrollY, stickyTop, insertPlaceholder), {
     passive: true,
   });
 };