Handling Memory Leaks in React with Event Listeners in Functional Components
I'm working through a tutorial and I'm experiencing memory leaks in my React application that uses functional components with hooks... I've set up an event listener for a scroll event that updates a state variable, but I'm noticing that the listener isn't being cleaned up properly, leading to increased memory usage on subsequent renders. I've implemented it like this: ```javascript import React, { useEffect, useState } from 'react'; const ScrollComponent = () => { const [scrollY, setScrollY] = useState(0); useEffect(() => { const handleScroll = () => { setScrollY(window.scrollY); }; window.addEventListener('scroll', handleScroll); // I thought this cleanup would work // but it seems the listener continues return () => { window.removeEventListener('scroll', handleScroll); }; }, []); // empty dependency array return <div>Scroll Position: {scrollY}</div>; }; export default ScrollComponent; ``` Despite including the cleanup function in the `useEffect`, the memory usage keeps increasing when navigating between different components that utilize `ScrollComponent`. I'm using React 17.0.2 and it's deployed on a Next.js framework. I've also checked for other potential memory leaks by disabling other effects and inspecting component unmounting, but I need to seem to isolate the scenario. I'm getting the following warning in the console about memory usage: ``` Warning: Each child in a list should have a unique "key" prop. ``` Could the scenario be related to how the event listener is being handled, or is there something else I might be missing? Any insights on how to properly manage event listeners in functional components to avoid these memory leaks would be greatly appreciated! I'm coming from a different tech stack and learning Javascript.