| 1 | --- |
| 2 | title: Use useDeferredValue for Expensive Derived Renders |
| 3 | impact: MEDIUM |
| 4 | impactDescription: keeps input responsive during heavy computation |
| 5 | tags: rerender, useDeferredValue, optimization, concurrent |
| 6 | --- |
| 7 | |
| 8 | ## Use useDeferredValue for Expensive Derived Renders |
| 9 | |
| 10 | When user input triggers expensive computations or renders, use `useDeferredValue` to keep the input responsive. The deferred value lags behind, allowing React to prioritize the input update and render the expensive result when idle. |
| 11 | |
| 12 | **Incorrect (input feels laggy while filtering):** |
| 13 | |
| 14 | ```tsx |
| 15 | function Search({ items |
| 16 | const [query, |
| 17 | const filtered = |
| 18 | |
| 19 | return ( |
| 20 | <> |
| 21 | <input value={ |
| 22 | <ResultsList results= |
| 23 | </> |
| 24 | ); |
| 25 | } |
| 26 | ``` |
| 27 | |
| 28 | **Correct (input stays snappy, results render when ready):** |
| 29 | |
| 30 | ```tsx |
| 31 | function Search({ items |
| 32 | const [query, |
| 33 | const deferredQuery = |
| 34 | const filtered = |
| 35 | () => items. |
| 36 | [items, deferredQuery] |
| 37 | ); |
| 38 | const isStale = |
| 39 | |
| 40 | return ( |
| 41 | <> |
| 42 | <input value={ |
| 43 | <div style={ |
| 44 | <ResultsList results= |
| 45 | </div> |
| 46 | </> |
| 47 | ); |
| 48 | } |
| 49 | ``` |
| 50 | |
| 51 | **When to use:** |
| 52 | |
| 53 | - Filtering/searching large lists |
| 54 | - Expensive visualizations (charts, graphs) reacting to input |
| 55 | - Any derived state that causes noticeable render delays |
| 56 | |
| 57 | **Note:** Wrap the expensive computation in `useMemo |
| 58 | |
| 59 | Reference: [React useDeferredValue](https://react.dev/reference/react/useDeferredValue |