How do we know when the state changes? We subscribe!

subscribe.js

const state = {};
const listeners = [];

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

const dispatch = (action/change) => {
  const newState = getNewState(state, action);
  state = newState;
  listeners.forEach(listener => {
    listener(state)
  });
};


const action = { type: 'ADD_TODO', change: 'Go to the cafe' };
dispatch(action)
const listener = (newState) => {
  // Do something after knowing the change
};

subscribe(listener);