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963 markdown files reformatted with the repository's pinned prettier so pnpm format:check covers the folded tree like every other repo file. The formatter's embedded-language pass also normalized code fences (TS semicolons, closed HTML tags in examples, lowercased CSS hex colors, one renumbered list that skipped an index). Alphanumeric token deltas vs the fold commit were audited file-by-file; all are formatter-equivalent markup normalizations plus the four sanitized skills.
1.2 KiB
1.2 KiB
title, impact, impactDescription, tags
| title | impact | impactDescription | tags |
|---|---|---|---|
| Calculate Derived State During Rendering | MEDIUM | avoids redundant renders and state drift | rerender, derived-state, useEffect, state |
Calculate Derived State During Rendering
If a value can be computed from current props/state, do not store it in state or update it in an effect. Derive it during render to avoid extra renders and state drift. Do not set state in effects solely in response to prop changes; prefer derived values or keyed resets instead.
Incorrect (redundant state and effect):
function Form() {
const [firstName, setFirstName] = useState('First');
const [lastName, setLastName] = useState('Last');
const [fullName, setFullName] = useState('');
useEffect(() => {
setFullName(firstName + ' ' + lastName);
}, [firstName, lastName]);
return <p>{fullName}</p>;
}
Correct (derive during render):
function Form() {
const [firstName, setFirstName] = useState('First');
const [lastName, setLastName] = useState('Last');
const fullName = firstName + ' ' + lastName;
return <p>{fullName}</p>;
}
References: You Might Not Need an Effect