index.js

//////// Background Scripts Entry, index.js ////////
import { createBackgroundStore } from 'redux-webext';
import { createSubscriber } from './universalStore';

createBackgroundStore({ ... }).then((store) => {
  // create subscriber immediately!!
  store.subscribe(createSubscriber(store));
  // ...
});


//////// universalStore.js ////////
import { createDomainListener } from './listener/domain';

export const createSubscriber = (store) => {
  const domainListener = createDomainListener(store);  // listener for domain change

  return () => { // when state change, this function will be called
    const state = store.getState();
    domainListener(state.domain);
  }
}


//////// domain.js ////////
export const createDomainListener = (store) => {
  let domain = store.getState().domain;
  return (nextDomain) => {
    if (nextDomain !== domain) { // domain change
      store.dispatch(someAction());
      // ....
    }
  };
}