Learning Redux

Handling other actions (updating the present state)

This is the tricky part--now we need to delegate handling the action to the reducer that we got as an argument. Then, we will use its result to insert a new present state.

Replace the return state // TODO line below default: by doing the following:

1. First, we call the reducer function with the current present state and the action we received. The result is stored in a newPresent constant:

        const newPresent = reducer(present, action)

2. Next, we compare the new present to the old present; if they are the same, we simply return the current state. This prevents unnecessary additions to the history:

        if (present === newPresent) {          return state        }

3. Otherwise, we create a new past array from the ...