I just had a quick look, some observations if you don't mind, - use a good linter and fix all warnings you get from it if possible - use code formatting so al

I just had a quick look, some observations if you don't mind, - use a good linter and fix all warnings you get from it if possible - use code formatting so all your code has the same formatting - you put the isDead function in the Piece class and pass the board object, IMO it makes more sense to put it in the Board class or even better make a Game/Puzzle class , then you can reuse the Board and Piece unchanged when you implement different rules but the board and pieces are the same.