fix: back-to-top falsely initialized when not needed

Former-commit-id: 7bb90fc88eaac8767f0f5f780cc2b3a9f6c5f3fe

1 files changed, 51 insertions, 48 deletions

diff --git a/assets/js/back2top.js b/assets/js/back2top.js
index 86f8d11d..6d7501e1 100644
--- a/assets/js/back2top.js
+++ b/assets/js/back2top.js
@@ -6,52 +6,55 @@ const backToTopButton = document.getElementById("back2top-button")
 const backToTopInstruction = document.getElementById("back2top-instruction")
 const seenAndUsedBat = localStorage.getItem("geedeapro.ui.seenAndUsedBat")
 
-function hideInstruction() {
-  backToTopInstruction.remove()
+if (backToTopInstruction && backToTopButton) {
+    function hideInstruction() {
+        backToTopInstruction.remove()
+    }
+    if (seenAndUsedBat) hideInstruction()
+
+    // listen to button click and scroll to top
+    backToTopButton.addEventListener("click", () => {
+      window.scrollTo({ top: 0, behavior: "smooth" })
+      if (!seenAndUsedBat) {
+        localStorage.setItem("geedeapro.ui.seenAndUsedBat", true);
+        hideInstruction();
+      }
+    })
+
+    // listen to scroll and toggle button visibility
+    let lastOffset = window.scrollY
+
+    window.addEventListener("scroll", () => {
+      const offset = window.scrollY
+      const batIsHidden = backToTop.classList.contains("-top-25")
+      const enoughHeight = offset >= 2000
+      const isScrollingUp = offset < lastOffset
+      const isScrollingDown = offset > lastOffset
+
+      function hide() {
+        backToTop.classList.remove("top-0")
+        backToTop.classList.add("-top-25")
+        backToTop.classList.remove("animate-head-shake")
+      }
+
+      function show() {
+        backToTop.classList.remove("-top-25")
+        backToTop.classList.add("top-0")
+        backToTop.classList.add("animate-head-shake")
+      }
+
+      if (enoughHeight && isScrollingUp && batIsHidden) {
+        // show only when scrolling up
+        show()
+      } else if (isScrollingDown && !batIsHidden) {
+        // hide as soon as user scrolls down again
+        hide()
+      }
+
+      // hide no matter what if too close to top
+      if (!enoughHeight) hide()
+
+      lastOffset = offset
+    })
 }
-if (seenAndUsedBat) hideInstruction()
-
-// listen to button click and scroll to top
-backToTopButton.addEventListener("click", () => {
-  window.scrollTo({ top: 0, behavior: "smooth" })
-  if (!seenAndUsedBat) {
-    localStorage.setItem("geedeapro.ui.seenAndUsedBat", true);
-    hideInstruction();
-  }
-})
-
-// listen to scroll and toggle button visibility
-let lastOffset = window.scrollY
-
-window.addEventListener("scroll", () => {
-  const offset = window.scrollY
-  const batIsHidden = backToTop.classList.contains("-top-25")
-  const enoughHeight = offset >= 2000
-  const isScrollingUp = offset < lastOffset
-  const isScrollingDown = offset > lastOffset
-
-  function hide() {
-    backToTop.classList.remove("top-0")
-    backToTop.classList.add("-top-25")
-    backToTop.classList.remove("animate-head-shake")
-  }
-
-  function show() {
-    backToTop.classList.remove("-top-25")
-    backToTop.classList.add("top-0")
-    backToTop.classList.add("animate-head-shake")
-  }
-
-  if (enoughHeight && isScrollingUp && batIsHidden) {
-    // show only when scrolling up
-    show()
-  } else if (isScrollingDown && !batIsHidden) {
-    // hide as soon as user scrolls down again
-    hide()
-  }
-
-  // hide no matter what if too close to top
-  if (!enoughHeight) hide()
-
-  lastOffset = offset
-})
+