All 5 useReducer & Complex State Logic questions
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When should you choose useReducer over useState for managing a component's state? What is the basic structure of a reducer function used with the useReducer hook? How would you manage a multi step form's state using useReducer instead of several separate useState calls? How would you combine useReducer with the Context API to share complex state across many components?
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How do you pass extra data along with an action when using useReducer?

Intermediate

Answer

An action object can include any additional properties beyond just its type, commonly called a payload, letting the reducer know exactly what data it needs to correctly compute the new state for that specific action.
function reducer(state, action) {
  switch (action.type) {
    case 'addItem':
      return { items: [...state.items, action.payload] };
    default:
      return state;
  }
}

dispatch({ type: 'addItem', payload: { id: 1, name: 'Apple' } });
Real-world example A shopping cart reducer receives the specific item being added as a payload inside the dispatched action, letting it correctly add exactly that item to the existing list of cart items.

Common follow-ups: Is there a required naming convention for the extra data included in an action?;How would you dispatch multiple different pieces of data together in a single action?

State Management;Design Patterns in React
All 5 useReducer & Complex State Logic questions