Removing Effect dependencies in code
useEffect(() => {
setCount(count => count + 1);
}, []);Read the example from data and control flow to the resulting UI. Keep the component boundary small.
Back to week 2
Topic
Removing Effect dependencies
Definition
Effect dependencies must include reactive values read by an Effect; restructure code rather than suppressing dependencies when that causes unwanted reruns.
In simpler words
Move static values outside, use updater functions, or separate events so the dependency list matches reality.
Dependency honesty, stable values, and avoiding stale closures.
After this you can
- Fix dependency warnings without disabling the linter.
- Explain the trade-off to a teammate using a small example.
- Name at least one common bug pattern for this topic.
Understand Removing Effect dependencies
Dependency honesty, stable values, and avoiding stale closures.
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 Removing Effect dependencies
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: eslint-disable on deps
// Wrong
useEffect(() => { save(draft); }, []); // draft omitted
// Right
// save from the submit event, or include draft intentionallyDo not hide changing inputs.
Mistake: Unstable function dep every render
// Wrong
useEffect(() => { load(fn); }, [fn]);
// fn recreated each render
// Right
// define fn with useCallback, or move load into the eventUnstable deps cause Effect storms.
Mistake: New object literal as dep
// Wrong
useEffect(() => {}, [{ status }]);
// Right
useEffect(() => {}, [status]);Depend on primitives or stable references.
Live playground
Removing Effect dependencies sandbox
Change one input at a time and predict the next render.
Effect runs: 0 (only when userId changes)
Do not omit deps you read — restructure instead.
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