Simple Redux-like Store

Store.js

class Store {
  constructor(reducer, initialState) {
    this.state = initialState;
    this.reducer = reducer;
    this.trigger = () => null;
  }

  subscribe(callback) {
    this.trigger = callback;
  }

  getState() {
    return this.state;
  }

  dispatch(action) {
    this.state = this.reducer(this.state, action);
    this.trigger();
  }
}

const ADD = 'ADD';
const DELETE = 'DELETE';

const reducer = (state, action) => {
  switch (action.type) {
    case ADD:
      return state + 1;
    case DELETE:
      return state - 1;
    default:
      return state;
  }
};

const store = new Store(reducer, 0);

store.subscribe(() => {
  console.log('Next State', store.getState());
});

store.dispatch({ type: ADD });
store.dispatch({ type: ADD });
store.dispatch({ type: ADD });

store.dispatch({ type: DELETE });
store.dispatch({ type: DELETE });
store.dispatch({ type: DELETE });