Othello: read the board

Black moves first. Click a gold dot to place a disc and flip every uninterrupted line of opposing discs bracketed by your own. Gold dots show legal moves. A player with no legal move passes automatically; the game ends when neither player can move. The larger disc count wins.

The Prelude contains the directional scan, move validation and board update. The ordinary cells hold the board, disc counts and turn: p = 1 means black, p = -1 means white, and p = 0 means game over. Press Restart for a new game.