ReddRadar
Agent skill
using-reducers
Teaches useReducer for complex state logic in React 19. Use when state updates depend on previous state, multiple related state values, or complex update logic.
Install this agent skill to your Project
npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/data/using-reducers
SKILL.md
useReducer Patterns
When to Use useReducer
Use useReducer when:
- Multiple related state values
- Complex state update logic
- Next state depends on previous state
- State transitions follow patterns
Use useState when:
- Simple independent values
- Basic toggle or counter logic
- No complex interdependencies
Basic Pattern
import { useReducer } from 'react';
const initialState = { count: 0, step: 1 };
function reducer(state, action) {
switch (action.type) {
case 'increment':
return { ...state, count: state.count + state.step };
case 'decrement':
return { ...state, count: state.count - state.step };
case 'setStep':
return { ...state, step: action.payload };
case 'reset':
return initialState;
default:
throw new Error(`Unknown action: ${action.type}`);
}
}
function Counter() {
const [state, dispatch] = useReducer(reducer, initialState);
return (
<>
<p>Count: {state.count}</p>
<p>Step: {state.step}</p>
<button onClick={() => dispatch({ type: 'increment' })}>+</button>
<button onClick={() => dispatch({ type: 'decrement' })}>-</button>
<input
type="number"
value={state.step}
onChange={(e) => dispatch({ type: 'setStep', payload: +e.target.value })}
/>
<button onClick={() => dispatch({ type: 'reset' })}>Reset</button>
</>
);
}
Complex Example: Todo List
const initialState = {
todos: [],
filter: 'all',
};
function todosReducer(state, action) {
switch (action.type) {
case 'added':
return {
...state,
todos: [...state.todos, { id: Date.now(), text: action.text, done: false }],
};
case 'toggled':
return {
...state,
todos: state.todos.map(t =>
t.id === action.id ? { ...t, done: !t.done } : t
),
};
case 'deleted':
return {
...state,
todos: state.todos.filter(t => t.id !== action.id),
};
case 'filterChanged':
return {
...state,
filter: action.filter,
};
default:
throw new Error(`Unknown action: ${action.type}`);
}
}
For comprehensive useReducer patterns, see: research/react-19-comprehensive.md lines 506-521.
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