A (ultra) simple implementation of a Redux app using the ES6 syntax.

counter_reduxy.js

// A crude implementation of a Redux store
// It keeps track of the state of the application and calls the listeners
// whenever there's a action dispatch
const createStore = (reducer) => {
  let state;
  const listeners = [];

  const getState = () => state;

  const dispatch = (action) => {
    state = reducer(state, action);
    listeners.forEach(listener => listener());
  };

  const subscribe = (listener) => listeners.push(listener);

  // dispatch an empty action in order to start the initial state
  dispatch({ });

  return { getState, dispatch, subscribe };
};

// the reducer is a pure function which is the responsible for changing
//  the state of the application (without mutating the parameters)
const counter = (state = 0, action) => {
  switch (action.type) {
    case 'INCREMENT':
      return state + 1;
    case 'DECREMENT':
      return state - 1;
    default:
      return state;
  }
};

const store = createStore(counter);
const render = () => document.body.innerText = store.getState();

store.subscribe(render);
render();

// bind events to dispatch actions
// Left-click to increment the counter
document.addEventListener('click', () => store.dispatch({ type: 'INCREMENT' }) );
// Right-click to decrement the counter
document.addEventListener('contextmenu', (event) => {
  event.preventDefault();
  store.dispatch({ type: 'DECREMENT' });
});