iamhenry React Patterns
Overview
Decision-driven guidance for writing idiomatic React. Focus on avoiding common anti-patterns and choosing the right tool for each job.
Quick Decision Trees
Should This Be a useEffect?
Is this synchronizing with an EXTERNAL system?
├─ YES (DOM, network, third-party widget) → useEffect
└─ NO
├─ Caused by USER ACTION? → Event handler
├─ Can be CALCULATED from state/props? → Render-time calculation
└─ Runs because component DISPLAYED? → useEffect
Should This Be State?
Can it be computed from existing props/state?
├─ YES → Derive it (const x = ...)
└─ NO
├─ Does it change over time? → useState
└─ NO → Regular variable or prop
Should I Memoize This?
Is the calculation expensive (>1ms)?
├─ NO → Don't memoize
└─ YES
├─ Used in render? → useMemo
└─ Passed to child as prop? → Consider useMemo
Anti-Pattern Quick Reference
| BAD | GOOD | Reference |
|---|---|---|
| Derived state in useEffect | Calculate during render | references/effects.md |
| useEffect for event logic | Put in event handler | references/effects.md |
| useEffect to reset state on prop | Use React key prop |
references/effects.md |
| Effect chains (A→B→C) | Calculate in single handler | references/effects.md |
| Notify parent via useEffect | Call in same event handler | references/effects.md |
| Store full object when ID suffices | Store ID, derive object | references/state.md |
| Prop drilling 5+ levels | Composition or context | references/components.md |
| useMemo/useCallback everywhere | Only when measurably needed | references/performance.md |
| Inline handlers causing re-renders | useCallback IF measured issue | references/performance.md |
| Logic in onClick directly | Extract to named handler | references/events.md |
When to Load References
Load the specific reference file when working on that area:
- Effects issues:
Read(.agents/skills/react-patterns/references/effects.md) - State structure:
Read(.agents/skills/react-patterns/references/state.md) - Component design:
Read(.agents/skills/react-patterns/references/components.md) - Performance:
Read(.agents/skills/react-patterns/references/performance.md) - Event handling:
Read(.agents/skills/react-patterns/references/events.md)
Core Principles
- Effects are escape hatches - Only for external system sync
- Derive, don't sync - If computable, compute it
- State should be minimal - Store IDs not objects, derive the rest
- Measure before optimizing - No premature useMemo/useCallback
- Colocate related logic - Keep cause and effect together
- Data flows down - Avoid passing data up via Effects