React useMemo not preventing re-renders in functional component when using complex dependencies
I'm performance testing and I'm collaborating on a project where I'm not sure how to approach I'm refactoring my project and I'm using React 17 with functional components and I've come across an scenario where `useMemo` isn't behaving as expected. I have a component that renders a list of items based on a complex calculation. The list is derived from a large dataset, and I want to optimize performance by memoizing the result of this calculation. However, even when using `useMemo`, my component still re-renders every time the parent component updates, which is causing performance optimization. Here’s a simplified version of my component: ```javascript import React, { useMemo } from 'react'; const ItemList = ({ items, filter }) => { const filteredItems = useMemo(() => { console.log('Calculating filtered items...'); return items.filter(item => item.name.includes(filter)); }, [items, filter]); return ( <ul> {filteredItems.map(item => ( <li key={item.id}>{item.name}</li> ))} </ul> ); }; export default ItemList; ``` In this example, I expect `Calculating filtered items...` to log only when `items` or `filter` changes, but it seems to re-calculate whenever the parent component renders, even if those dependencies haven’t changed. I’ve tried moving `useMemo` into the parent component, but the scenario continues. I've also checked that my `items` array is not being recreated on each render by wrapping it in `useMemo` in the parent, but still no luck. The parent component looks like this: ```javascript const ParentComponent = () => { const [filter, setFilter] = useState(''); const items = useMemo(() => getItems(), []); // getItems() fetches data once return <ItemList items={items} filter={filter} />; }; ``` Could the question be related to how React compares the `items` array? Is there a specific way I should structure my code to ensure that `useMemo` functions as intended? Any suggestions would be greatly appreciated! Has anyone dealt with something similar? I'm using Javascript 3.10 in this project. Hoping someone can shed some light on this. Has anyone dealt with something similar? I'm using Javascript 3.10 in this project. I'd really appreciate any guidance on this.