you-might-not-need-a-memo

# You Might Not Need a Memo Arguments: - scope: what to analyze (default: your current changes). Examples: "diff to staging", "PR #123", "src/components/", "whole codebase" - fix: whether to apply fixes (default: true). Set to false to only propose changes. User arguments: $ARGUMENTS ## References Read before analyzing: 1. https://overreacted.io/before-you-memo/ — two techniques to avoid memo entirely ## Anti-patterns to detect 1. **Wrapping a slow component in React.memo when state can be moved down**: If a component re-renders because of state it doesn't use, move that state into a smaller child component instead of memoizing. The slow component stops re-rendering without memo. 2. **Wrapping in React.memo when children can be lifted up**: If a parent owns state that changes frequently, extract the stateful part and pass the expensive subtree as `children`. Children passed as props don't re-render when the parent's state changes. 3. **useMemo on cheap computations**: Filtering or mapping a small array, string concatenation, simple arithmetic — these don't need memoization. Only memoize when you've measured a performance problem. 4. **useMemo with constantly-changing deps**: If the dependency array changes on every render, useMemo does nothing — it recalculates every time. Fix the deps or remove the memo. 5. **useMemo to create objects/arrays passed as props**: Instead of memoizing to prevent child re-renders, consider whether the child even needs referential stability. If the child doesn't use React.memo or pass it to a dep array, the memo is wasted. 6. **React.memo on components that always receive new props**: If the parent always passes new objects, arrays, or callbacks, React.memo's shallow comparison always fails. Fix the parent instead of memoizing the child. 7. **useMemo for derived state**: If you're computing a value from props or state, just compute it inline during render. React renders are fast. `const fullName = first + ' ' + last` doesn't need useMemo. ## Patterns that ARE correct — do not flag - A `useMemo` that builds a lookup `Map`/`Set` or a single-pass partition for list rendering (`.claude/rules/sim-components.md` "List-render performance"). ## Steps 1. Read the reference above to understand the two core techniques (move state down, lift content up) 2. Analyze the specified scope for the anti-patterns listed above 3. If fix=true, apply the fixes. If fix=false, propose the fixes without applying.