Topic
Definition
DOM refs provide imperative access to a rendered DOM element for focused integration work such as focus, scroll, or measurement.
In simpler words
Most UI should be declarative, but a ref is the right bridge when the browser API needs the real element.
Ref assignment, focus management, and avoiding DOM conflicts.
Ref assignment, focus management, and avoiding DOM conflicts.
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.
const inputRef = useRef<HTMLInputElement>(null);
<button onClick={() => inputRef.current?.focus()}>Focus</button>;Read the example from data and control flow to the resulting UI. Keep the component boundary small.
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?
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.
// Wrong
ref.current!.textContent = title;
// Right
return <p ref={ref}>{title}</p>;Declare UI from state; refs are for imperative browser APIs.
// Wrong
function Field() {
const ref = useRef(null);
ref.current?.focus();
return <input ref={ref} />;
}
// Right
useEffect(() => { ref.current?.focus(); }, []);
// or on user actionUnconditional focus fights the user and accessibility.
// Wrong
// keep element reference in a module variable
// Right
// read ref.current only while mounted; null on cleanup if neededDo not use DOM nodes after unmount.
Live playground
Change one input at a time and predict the next render.
inputRef.current?.focus()
Test
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