| 1 | --- |
| 2 | title: Use useRef for Transient Values |
| 3 | impact: MEDIUM |
| 4 | impactDescription: avoids unnecessary re-renders on frequent updates |
| 5 | tags: rerender, useref, state, performance |
| 6 | --- |
| 7 | |
| 8 | ## Use useRef for Transient Values |
| 9 | |
| 10 | When a value changes frequently and you don't want a re-render on every update (e.g., mouse trackers, intervals, transient flags), store it in `useRef` instead of `useState`. Keep component state for UI; use refs for temporary DOM-adjacent values. Updating a ref does not trigger a re-render. |
| 11 | |
| 12 | **Incorrect (renders every update):** |
| 13 | |
| 14 | ```tsx |
| 15 | function Tracker() { |
| 16 | const [lastX, |
| 17 | |
| 18 | useEffect(() => |
| 19 | const onMove = |
| 20 | window.addEventListener("mousemove |
| 21 | return () => |
| 22 | }, []); |
| 23 | |
| 24 | return ( |
| 25 | <div |
| 26 | style={{ |
| 27 | position: "fixed", |
| 28 | top: 0, |
| 29 | left: lastX, |
| 30 | width: 8, |
| 31 | height: 8, |
| 32 | background: "black", |
| 33 | }} |
| 34 | /> |
| 35 | ); |
| 36 | } |
| 37 | ``` |
| 38 | |
| 39 | **Correct (no re-render for tracking):** |
| 40 | |
| 41 | ```tsx |
| 42 | function Tracker() { |
| 43 | const lastXRef = |
| 44 | const dotRef = |
| 45 | |
| 46 | useEffect(() => |
| 47 | const onMove = |
| 48 | lastXRef.current = |
| 49 | const node = |
| 50 | if (node) { |
| 51 | node.style.transform |
| 52 | } |
| 53 | }; |
| 54 | window.addEventListener("mousemove |
| 55 | return () => |
| 56 | }, []); |
| 57 | |
| 58 | return ( |
| 59 | <div |
| 60 | ref={dotRef} |
| 61 | style={{ |
| 62 | position: "fixed", |
| 63 | top: 0, |
| 64 | left: 0, |
| 65 | width: 8, |
| 66 | height: 8, |
| 67 | background: "black", |
| 68 | transform: "translateX(0px)", |
| 69 | }} |
| 70 | /> |
| 71 | ); |
| 72 | } |
| 73 | ``` |