How do the totalPoints keep updated using Guil's solution?

The Reduce method takes 2 arguments, accumulator and the item it is currently looping through in the array, so by returning total + player.score we are using dot notation on each player object in the array to get their individual scores. Each time reduce loops through, it adds the player score for the current array index to total. Then at the end once it has looped through the whole array, you have the total points for each player combined returned to your totalPoints variable. Now whenever you update a player score, that is changing the state, which makes the component re render and update the state, reflecting a new total for totalPoints. If you need me to clarify more please just ask! Hope this helps!