I did this for an Othello game back in the 90's. The state was encoded in the URL along with the players move. It seemed weird to encode a slightly different UR

I did this for an Othello game back in the 90's. The state was encoded in the URL along with the players move. It seemed weird to encode a slightly different URL for every move the player might click, but that also meant squares that were not legal moves didn't get a URL. And that meant the mouse pointer would change when you hovered over a valid square! Another trick was to return the updated board state, but also include an automatic reload after a few seconds with the computers next move already determined. This made it look like "thinking" was going on when in fact it was already decided when the board updated on players move ;-) This was all in a CGI script. As others have pointed out, it also supported "undo" via the back button. Fun.