Redux: Register a store Listener

• There's another method you have access to on the Redux store object is store.subscribe(). What this does is basically subscribe a function to your store that simply logs a message every time an action is received and the store is updated.
• FreeCodeCamp Code:

const ADD = 'ADD';

const reducer = (state = 0, action) => {
  switch(action.type) {
    case ADD:
      return state + 1;
    default:
      return state;
  }
};

const store = Redux.createStore(reducer);

// Global count variable:
let count = 0;

// Change code below this line

// Change code above this line

store.dispatch({type: ADD});
console.log(count);
store.dispatch({type: ADD});
console.log(count);
store.dispatch({type: ADD});
console.log(count);

• Basically what they want us to do is to write a callback function that increments the global variable count every time the store receives an action, and pass this function in to the store.subscribe() method.

• Answer:
  

let count = 0;

store.subscribe(function() {
  count += 1
})