react-frontend

React Frontend

Component TypeScript

• Extend native elements with ComponentPropsWithoutRef<'button'>, add custom props via intersection
• Use React.ReactNode for children, React.ReactElement for single element, render prop (data: T) => ReactNode
• Discriminated unions for variant props — TypeScript narrows automatically in branches
• Generic components: <T> with keyof T for column keys, T extends { id: string } for constraints
• Event types: React.MouseEvent<HTMLButtonElement>, FormEvent<HTMLFormElement>, ChangeEvent<HTMLInputElement>
• as const for custom hook tuple returns
• useRef<HTMLInputElement>(null) for DOM (use ?.), useRef<number>(0) for mutable values
• Explicit useState<User | null>(null) for unions/null
• useReducer actions as discriminated unions: { type: 'set'; payload: number } | { type: 'reset' }
• useContext null guard: throw in custom useX() hook if context is null

Effects Decision Tree

Effects are escape hatches — most logic should NOT use effects.

Need	Solution
Derived value from props/state	Calculate during render (useMemo if expensive)
Reset state on prop change	key prop on component
Respond to user event	Event handler
Notify parent of state change	Call onChange in event handler, or fully controlled component
Chain of state updates	Calculate all next state in one event handler
Sync with external system	Effect with cleanup

Effect rules:

• Never suppress the linter — fix the code instead
• Use updater functions (setItems(prev => [...prev, item])) to remove state dependencies
• Move objects/functions inside effects to stabilize dependencies
• useEffectEvent for non-reactive values (e.g., theme in a connection effect)
• Always return cleanup for subscriptions, connections, listeners
• Data fetching: use ignore flag pattern or React Query

State Management

Local UI state       → useState, useReducer
Shared client state  → Zustand (simple) | Redux Toolkit (complex)
Atomic/granular      → Jotai
Server/remote data   → React Query (TanStack Query)
URL state            → nuqs, router search params
Form state           → React Hook Form