<p></p>
<p><b>@hlfan</b> commented on this pull request.</p>

<hr>

<p>In <a href="https://github.com/openstreetmap/openstreetmap-website/pull/5826#discussion_r2004502709">app/assets/javascripts/index/history.js</a>:</p>
<pre style='color:#555'>> +    changesetIntersectionObserver = new IntersectionObserver((entries) => {
+      if (ignoreIntersectionEvents) {
+        ignoreIntersectionEvents = false;
+        return;
+      }
+
+      let closestTargetToTop,
+          closestDistanceToTop = Infinity,
+          closestTargetToBottom,
+          closestDistanceToBottom = Infinity;
+
+      for (const entry of entries) {
+        if (entry.isIntersecting) continue;
+
+        const distanceToTop = entry.rootBounds.top - entry.boundingClientRect.bottom;
+        const distanceToBottom = entry.boundingClientRect.top - entry.rootBounds.bottom;
+        if (distanceToTop >= 0 && distanceToTop < closestDistanceToTop) {
+          closestDistanceToTop = distanceToTop;
+          closestTargetToTop = entry.target;
+        }
+        if (distanceToBottom >= 0 && distanceToBottom <= closestDistanceToBottom) {
+          closestDistanceToBottom = distanceToBottom;
+          closestTargetToBottom = entry.target;
+        }
+      }
+
+      if (closestTargetToTop && closestDistanceToTop < closestDistanceToBottom) {
+        const id = $(closestTargetToTop).data("changeset")?.id;
+        if (id) {
+          OSM.router.replace(location.pathname + "?" + new URLSearchParams({ before: id }) + location.hash);
+        }
+      } else if (closestTargetToBottom) {
+        const id = $(closestTargetToBottom).data("changeset")?.id;
+        if (id) {
+          OSM.router.replace(location.pathname + "?" + new URLSearchParams({ after: id }) + location.hash);
+        }
+      }
+    }, { root: $("#sidebar")[0] });
</pre>
<p dir="auto">Does the callback need to be redefined every time?</p>

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