How to fix Cannot perform a state update inside a useReducer without dispatching an action in React

Examine your component code and look for any lines where you're modifying the state variable directly. Common patterns include:
- state.push(newItem)
- state.property = newValue
- state = newState (reassignment)

Check both the component body and any helper functions that receive state as an argument. Use your browser's developer tools to set breakpoints or add console logs to trace the origin of the mutation.

Instead of modifying state directly, create an action object and call dispatch. For example:

// ❌ Wrong
directUpdate = () => {
  state.count = state.count + 1;
};

// ✅ Correct
const increment = () => {
  dispatch({ type: 'INCREMENT' });
};

Ensure your reducer handles the action type appropriately, returning a new state object rather than mutating the existing one.

Verify that your reducer function includes a case for the dispatched action type and returns a new state object immutably. Example:

function reducer(state, action) {
  switch (action.type) {
    case 'INCREMENT':
      return { ...state, count: state.count + 1 };
    default:
      return state;
  }
}

Avoid side effects inside the reducer. If you need asynchronous operations, use middleware like Redux Thunk or move logic to action creators.

After making changes, run your application and verify that the error no longer appears. Test the state updates by interacting with your UI and confirming that the state changes as expected. Use React DevTools and Redux DevTools to inspect state changes and action history. Write unit tests for your reducer to ensure it handles actions correctly and immutably.