connectState that vaguely works like react-redux's `connect`

connectState.js

/* usage:
const dataSelector = state => {
  return state.foo.bar;
}

connectState(dataSelector)((newValue, prevValue) => {
  console.log('foo.bar changed from', prevValue, 'to', newValue);
});
*/

// const STORE = Redux.createStore(reducer);

connectState = dataSelector => {
  let prevState;
 
  return callback => {
    // store initial state
    let initState = dataSelector(window.appState.getState());

    // subscribe returns the unsubscribe function, so we have to store this
    var unsubscribe = STORE.subscribe(() => {
 
      // get slice of latest state using the provided `dataSelector` function
      let curState = dataSelector(STORE.getState());

      // use lodash.isEqual or Immutable.is or some other form of object comparison
      // if (slice of) state has changed, call the `callback` function with new and old states
      if (!isEqual(curState, prevState)) {

        callback(curState, prevState);
        
        // store currentState
        prevState = curState;
      }
    });

    // initial call when binding subscriber, this is optional
    callback(initState, prevState);
    
    // store initial state
    prevState = initState;

    return unsubscribe;
  };
};