Utility function to combine more reducers, assigned to single properties of state object.

Why

Sometimes reducer can become too long, with too much actions in a single switch statement.

This utility function is usefull to split reducer in multiple small reducers and assign them to single object property, making complex properties (array, object, etc) isolated with their single reducers.

Actions need to be UNIQUE across all reducers to make it work like the initial giant reducer.

It can be used with any reducers, so it work well with both Redux and reducers used with useReducer hook.

Example

interface ArrayType {
  id: number;
  name: string;
}

interface StateType {
  name: string;
  tables: ArrayType[];
}

const initialState: StateType = {
  name: 'Alex',
  tables: [],
};

const subReducer: Reducer<ArrayType[]> = (state, { type, name, id }): ArrayType[] => {
  switch (type) {
    case 'ADD': {
      return [...state, { id, name }];
    }
    case 'REMOVE': {
      return state.filter(t => t.id !== id);
    }
    default: {
      return state;
    }
  }
};

const mainReducer: Reducer<StateType> = (state, { type, name }): StateType => {
  switch (type) {
    case 'UPDATE_NAME': {
      return { ...state, name };
    }
    default: {
      return state;
    }
  }
};

const finalReducer = mergeReducers<StateType>(mainReducer, { tables: subReducer });

// Trigger main reducer action
finalReducer(initialState, { type: 'UPDATE_NAME', name: 'Pippo' });

// Trigger sub reducer action (to change tables property)
finalReducer(initialState, { type: 'ADD', name: 'Test', id: 1 });

// Using with useReducer
const SimpleComponent = () => {
  const [state, dispatch] = useReducer(finalReducer, initialState);
  
  dispatch({ type: 'UPDATE_NAME', name: 'Pippo' });
  
  dispatch({ type: 'ADD', name: 'Test', id: 1 });
}

Author

👤 Alex Ferreli

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