Code reviewHardcr-g392

Subject Memory leak listenersLevel Senior–Staff~22 minCommon in Code quality & review interviewsIndustries Software development

Question

Review this React TypeScript scroll hook.

What a strong answer looks like

Separate real bugs from style. Rank issues by severity, point at the root cause rather than the symptom, and suggest a concrete fix — specific and kind.

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Code to reviewtsx

1function useScrollDirection() {2  const [dir, setDir] = useState<'up' | 'down'>('up');3  const last = useRef(0);4 5  useEffect(() => {6    const onScroll = () => {7      const y = window.scrollY;8      setDir(y > last.current ? 'down' : 'up');9      last.current = y;10    };11    window.addEventListener('scroll', onScroll, { passive: true });12    return () => window.removeEventListener('scroll', onScroll);13  }, []);14 15  return dir;16}

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