redux createStore code

createStore.js

const createStore = (reducer) => {
  let state;
  let listeners = [];
  
  const getState = () => state;
  
  const dispatch = action => {
    state = reducer(state, action);
    listeners.forEach(l => l());
  }
  
  const subscribe = listener => {
    listeners.push(listener);
    return () => {
      listeners = listeners.filter(l => l !== listener);
    }
  }
  
  dispatch({});
  
  return {getState, dispatch, subscribe};
}