appState

appState.js

const darkTheme = {
  name: 'dark',
  background: 'black',
  text: 'white',
}

const lightTheme = {
  name: 'light',
  background: 'white',
  text: 'black',
}

function reducer(state, actionName, payload) {
  switch (actionName) {
    case 'toggleTheme':
      return {
        ...state,
        theme: state.theme.name === 'light' ? darkTheme : lightTheme,
      };
    default:
      throw new Error(`Action does not exist: ${actionName}`);
  }
}

const appState = new GlobalState(reducer, { theme: lightTheme });

export default appState;

Part of https://medium.com/@dominictobias/using-react-hooks-for-global-redux-stores-97c092afe210 article