btn back to top

assets/js/back-to-top.js

@@ -0,0 +1,24 @@
+export function backToTop(){
+  const btn = document.getElementById('btn--back-to-top');
+  if (!btn) return;
+
+  let lastY = window.scrollY;
+  let peakY = window.scrollY;
+
+  window.addEventListener('scroll', () => {
+    const currentY = window.scrollY;
+
+    if (currentY > lastY) {
+      peakY = currentY;
+      btn.classList.remove('is-visible');
+    } else {
+      if (currentY <= 800) {
+        btn.classList.remove('is-visible');
+      } else if (peakY - currentY >= 200 && peakY > 600) {
+        btn.classList.add('is-visible');
+      }
+    }
+
+    lastY = currentY;
+  }, { passive: true });
+}

assets/js/script.js

@@ -1,5 +1,6 @@
 import { headerToggle, headerScrollVisibility } from './header.js';
 import { copyLink } from './share.js';
+import { backToTop } from './back-to-top.js';
 import { themeToggle } from './themeToggle.js';
 import { playVideo } from './hero-video.js';
 import { initDropdowns } from './dropdown.js';
@@ -14,6 +15,7 @@ window.onload = async function () {
 
   headerToggle();
   themeToggle();
+  backToTop();
 
   copyLink();
   playVideo();