It is composed of two main components:
- Board - graphical go board implemented in HTML5 canvas. It has extensive API for easy manipulation. You can add and remove predefined objects like stones on board, you can create your own objects, or even make cut-outs of board.
- Game - object for storing of game's position and controlling game's flow. With method play you can play move and create new position with rules applied.
WGo.js also comes with powerful go player, or more precisely sgf game viewer.
You can get more info here: http://wgo.waltheri.net/