Redux Typescript - UI Reducers - TOGGLE / UPDATE for common UI States

app.consts.ts

export module UIConsts {
    export const UI_UPDATE = 'UI_UPDATE';
    export const TOGGLE_UI_STATE = 'TOGGLE_UI_STATE';
}

app.interfaces.ts

export interface StateAction {
    type: string;
    payload: any
}

ui.reducers.ts

import {StateAction} from '../app.interfaces';
import {UIConsts} from '../app.consts';
import * as _ from 'lodash';

// Examples:
export const INITIAL_STATE = {
  isItemListShowing: false,
  isNewItemCreated: false,
  isItemListLoading: false
}

export const UIReducer = (state: any = INITIAL_STATE, {type, payload}: StateAction) => {
    switch (type) {
        case UIConsts.UI_UPDATE:
            return _.assign({}, state, payload);

        case UIConsts.TOGGLE_UI_STATE:
            if (!payload.key)
                return state;
                
            let newState = {};
            newState[payload.key] = !_.get(state, payload.key);
            return _.assign({}, state, newState);    
    
        default:
            return state;
    }
};