Handling Prop Updates in React 18 When Using useMemo for Expensive Calculations
I'm experimenting with I'm facing an issue where my component is not re-rendering as expected when props change, even though I'm using `useMemo` to optimize an expensive calculation... I'm working with React 18 and have a parent component that passes down a value to a child component, which performs some heavy computation based on that value. I expected the child component to update whenever the prop changes, but it seems like the memoized value isn't recalculating correctly. Here’s a simplified version of my code: ```javascript import React, { useMemo } from 'react'; const ChildComponent = ({ data }) => { const expensiveCalculation = useMemo(() => { console.log('Calculating...'); // Simulate an expensive calculation return data.reduce((acc, item) => acc + item, 0); }, [data]); return <div>Calculated Value: {expensiveCalculation}</div>; }; const ParentComponent = () => { const [items, setItems] = React.useState([1, 2, 3]); const addItem = () => { setItems(prev => [...prev, prev.length + 1]); }; return ( <div> <ChildComponent data={items} /> <button onClick={addItem}>Add Item</button> </div> ); }; export default ParentComponent; ``` When I click the 'Add Item' button, I see the console log for 'Calculating...' only when the component first mounts, but not on subsequent updates. I’ve double-checked that I’m passing the updated `items` array to the `ChildComponent`. The `data` prop should change, and thus I expect `useMemo` to recalculate the `expensiveCalculation` value. I've tried using `JSON.stringify(data)` in the dependency array to see if that would trigger the recalculation, but even that didn’t resolve the issue. I’m unsure if I’m misunderstanding how `useMemo` works, or if there’s something else at play here. Any insights on why the memoized value isn't recalculating would be appreciated! Thanks for taking the time to read this! Thanks for taking the time to read this!