weiqi.js is an implementation of the board game Go. It provides mechanisms for representing a board with black and white stones, as well as the logic to actually play a game. The objects used in weiqi.js are persistent--methods often return entirely new instances instead of mutating internal state.

Persistence and structural sharing offer a memory-efficient way to represent multiple states of the board simutaneously, a desirable trait for applications where you'd like to explore the history of the game (such as for review) or to explore possible future responses (such as for AI decision-making).

The library is available as an npm package, and can be used in the browser with tools like browserify. If you don't want to use browserify, there is a pre-built file in the dist-browser directory that you can include in your browser-targeted projects right away. Access Weiqi with the global Weiqi variable in this case.

var Weiqi = require('weiqi');
var game = Weiqi.createGame(9);  // creates a game on a 9 x 9 board
game = Weiqi.createGame(13);  // creates a game on a 13 x 13 board
game = Weiqi.createGame(19);  // creates a game on a 19 x 19 board

var Weiqi = require('weiqi');
var game = Weiqi.createGame(9);
game = Weiqi.play(game, 'black', [2,2]);
game = Weiqi.play(game, 'white', [6,7]);
game = Weiqi.pass(game, 'black'); // black passes
game = Weiqi.pass(game, 'white'); // white passes

Weiqi.play and Weiqi.pass each take a player identifier ('black' or 'white'). Weiqi.play takes an additional zero-indexed array of size two that indicates the position to place a stone. Weiqi.play will raise exceptions for the following situations:

• the game is already over (there have already been two consecutive passes)
• it is not currently the turn of the player who is attempting to play
• the move violates positional superko (at the end of any turn, the board cannot be in a state in which it has been previously).

get('currentPlayer') returns either 'black' or 'white'.

> var Weiqi = require('weiqi');
> var game = Weiqi.play(Weiqi.createGame(9), 'black', [2,2]);
> game.get('currentPlayer');
"o"

isOver returns true iff there have been two consecutive passes.

> var Weiqi = require('weiqi');
> var game = Weiqi.play(Weiqi.createGame(9), 'black', [2,2]);
> Weiqi.isOver(game);
false
> game = Weiqi.pass(game, 'white');
> Weiqi.isOver(game);
false
> game = Weiqi.pass(game, 'black');
> Weiqi.isOver(game);
true

To compute the score of the game (using area score) pass a value of komi to areaScore(). All stones are considered alive.

Weiqi.areaScore(game, 7.5);  // compute area score given 7.5 komi