Infinite scrolling using nextjs16 and useInfiniteQuery (Tanstack)

Summary

Infinite scrolling in a Next.js 16 application using Tanstack Query’s useInfiniteQuery and the IntersectionObserver API failed due to improper handling of the observer target and race conditions during page transitions. The issue caused unexpected behavior in loading subsequent pages, leading to incomplete data rendering.

Root Cause

• Observer Target Mismanagement: The IntersectionObserver was not properly unobserved or re-observed when the target element changed or was removed from the DOM.
• Race Conditions: Concurrent fetches triggered by the observer led to inconsistent page loading states.
• Threshold Mismatch: The observer’s threshold value was set too low, causing premature triggering of the next page fetch.

Why This Happens in Real Systems

• Dynamic Content: Infinite scrolling relies on dynamically updating the DOM, making it prone to observer target inconsistencies.
• Asynchronous Nature: The asynchronous nature of useInfiniteQuery and IntersectionObserver can lead to race conditions if not properly synchronized.
• Browser Inconsistencies: Different browsers may handle intersection thresholds and observer callbacks differently, affecting reliability.

Real-World Impact

• User Experience Degradation: Incomplete or delayed data loading frustrates users.
• Performance Issues: Unnecessary fetches and re-renders increase resource consumption.
• Data Inconsistency: Race conditions can lead to missing or duplicated data.

Example or Code

"use client";
import { useInfiniteQuery } from "@tanstack/react-query";
import { getPosts } from "@/services/postApi";
import { useEffect, useRef } from "react";

export default function PostsClient() {
  const observerTarget = useRef(null);
  const POSTS_PER_PAGE = 10;

  const {
    data,
    isLoading,
    isError,
    error,
    fetchNextPage,
    hasNextPage,
    isFetchingNextPage,
  } = useInfiniteQuery({
    queryKey: ["posts"],
    queryFn: async ({ pageParam = 0 }) => {
      const allPosts = await getPosts();
      const start = pageParam * POSTS_PER_PAGE;
      const end = start + POSTS_PER_PAGE;
      return allPosts.slice(start, end);
    },
    initialPageParam: 0,
    getNextPageParam: (lastPage, allPages, lastPageParam) => {
      return lastPage.length  {
    const observer = new IntersectionObserver(
      (entries) => {
        if (entries[0].isIntersecting && hasNextPage && !isFetchingNextPage) {
          fetchNextPage();
        }
      },
      { threshold: 0.5 } // Increased threshold for stability
    );

    const currentTarget = observerTarget.current;
    if (currentTarget) {
      observer.observe(currentTarget);
    }

    return () => {
      if (currentTarget) {
        observer.unobserve(currentTarget);
      }
    };
  }, [fetchNextPage, hasNextPage, isFetchingNextPage]);

  if (isLoading) return 
Loading...
;
  if (isError) return 
{(error as Error).message}
;

  const allPosts = data?.pages.flatMap((page) => page) ?? [];

  return (
    
      {/* PostsList and other components */}
      

        {isFetchingNextPage && 
Loading more posts...
}
        {!hasNextPage && allPosts.length > 0 && 
No more posts to load
}