Simple Redux source code... kinda

redux.js

function createStore(reducer, initialState) {
  let currentState = initialState;
  let listeners = [];

  function getState() {
    return currentState;
  }

  function dispatch(action) {
    // Create the state from the reducer
    currentState = reducer(currentState, action);

    // Notify listeners
    listeners.forEach(listener => {
      listener();
    });

    return action;
  }

  function subscribe(callback) {
    listeners.push(callback);
  }

  return {
    getState,
    dispatch,
    subscribe,
  };
}