Referencing values with refs in code
const timerRef = useRef<number | null>(null);
timerRef.current = window.setTimeout(save, 500);Read the example from data and control flow to the resulting UI. Keep the component boundary small.
Back to week 2
Topic
Referencing values with refs
Definition
A ref is a mutable object whose current property persists between renders without causing a re-render when changed.
In simpler words
Use refs for values React does not need to display, such as timer IDs or a DOM node handle.
useRef, mutable current, and state versus refs.
After this you can
- Keep non-visual values without triggering UI updates.
- Explain the trade-off to a teammate using a small example.
- Name at least one common bug pattern for this topic.
Understand Referencing values with refs
useRef, mutable current, and state versus refs.
Start by identifying which value or browser behavior changes. Then describe the UI from that current input instead of editing the DOM as a separate source of truth.
Apply Referencing values with refs
Keep rendering as a calculation. Put user-triggered changes in event handlers, preserve UI memory in state, and reserve external synchronization for Effects or the server-state layer.
Name values by their UI meaning, test the loading and error path when data is remote, and avoid keeping two editable copies of the same value.
Ask before adding code: is this local UI memory, shared client state, or Nest-owned server state?
Where bugs hide
Definition
High-bug areas are places where a small API misuse looks correct but produces stale UI, duplicate work, or silent failures.
In simpler words
Each mistake below shows Wrong vs Right code — compare them side by side.
When something misbehaves, match the symptom to a pattern below before rewriting the feature.
Prefer fixing the ownership or update path over adding another Effect or sync step.
Mistake: Drive UI from ref.current in render
// Wrong
const n = useRef(0);
return <p>{n.current}</p>; // won't update on n.current++
// Right
const [n, setN] = useState(0);
return <p>{n}</p>;Visible values need state.
Mistake: Expect ref writes to re-render
// Wrong
ref.current += 1; // screen unchanged
// Right
setCount(c => c + 1);Refs skip re-render by design.
Mistake: Server data only in a ref
// Wrong
const cache = useRef([]);
cache.current = await list();
// Right
useQuery({ queryKey: ["tickets"], queryFn: list })Refs are not a persistence or server cache layer.
Live playground
Referencing values with refs sandbox
Change one input at a time and predict the next render.
ref.current = 0 · renders = 0
const clicks = useRef(0);
Keep in mind
- Keep the formal definition in mind; it explains which tool belongs where.
- Prefer one source of truth over synchronized copies of the same value.
- When behavior surprises you, trace: input → update → render → committed UI.
- Study the Wrong vs Right examples in “Where bugs hide” before you merge.
Test
Check your understanding
At least 10 questions — mix of concept, syntax, practical, and logic. Score ≥ 80% (enforced by the API) to save progress.
Checking your session…
10 questions · concept 3 · syntax 3 · practical 2 · logic 2