Offer legal moves

Ask the native engine

A placement game uses legalPoints and playMove. A moving-piece game uses turnChoices, pieceMoves and movePiece. Narrowing to compulsory captures belongs to the engine; a host should display its answers.

import {createGame,turnChoices,pieceMoves,movePiece} from "@johnmorrisdotca/narabe";
let game = createGame({variant:"checkers"});
const choices = turnChoices(game);
if (choices?.kind === "move" && choices.pieces.length) {
  const from = choices.pieces[0];
  const to = pieceMoves(game,from)[0];
  game = movePiece(game,from,to);
}
console.log(game.moves.length,game.toPlay);

1 white

Handle the other phases

turnChoices returns null for finished games, owed quadrant turns, queued-piece games and Go. Null does not always mean the game ended. Use canTwist/twistBoard for a quarter turn, piecePlacements/placePiece for a queue, and canPass/passTurn for passes. A swap opening may instead need canChooseColour/chooseColour or canExtendOpening/extendOpening.

Keep the whole turn

A game may place multiple stones, demand a twist or continue a capture chain. Read toPlay, pendingTwist, chainAt and opening state after every action rather than assuming each click passes the turn. forbiddenReason explains a forbidden shape, while other refusals can come from occupancy, phase or board bounds. See state design.