React 18: Using useMemo for Expensive Calculations in Conditional Rendering Leads to Stale Data
I'm stuck on something that should probably be simple. I'm facing an issue with using `useMemo` in my React 18 application. I have a component that conditionally renders expensive calculations based on user input. However, it seems that my memoized value is stale and doesn't update as expected when the dependencies change. Here's a simplified version of my code: ```javascript import React, { useState, useMemo } from 'react'; const ExpensiveComponent = ({ input }) => { const calculateValue = (num) => { console.log('Calculating...'); // To track recalculations return num * 1000; }; const memoizedValue = useMemo(() => calculateValue(input), [input]); return <div>Calculated Value: {memoizedValue}</div>; }; const ParentComponent = () => { const [input, setInput] = useState(0); return ( <div> <input type='number' value={input} onChange={e => setInput(parseInt(e.target.value, 10))} /> <ExpensiveComponent input={input} /> </div> ); }; export default ParentComponent; ``` I expected that every time I change the input, `calculateValue` should re-run, but instead, it's using the stale value from the previous render unless I force a re-render by changing state elsewhere. This issue doesn't happen if I directly call `calculateValue(input)` in the render. I've also checked that the `input` value is indeed changing as expected. Could it be that `useMemo` is caching the result even when the dependencies change? I’ve tried resetting the memoization by switching the dependencies, but that didn’t help. Is there a specific pattern or best practice I should follow to avoid this stale value issue when using `useMemo` in conditional rendering scenarios? I'm working on a application that needs to handle this. Could this be a known issue?