chess.onclick = function (event) {var x = event.offsetX; var y = event.offsetY; var xb = (x-15)%30; var yb = (y-15)%30;if (xb>11&&xb<19||yb>11&&yb<19) {return;}var i = Math.floor(x/30); var j = Math.floor(y/30); if(chessBoard[i][j] == 0){ paintPieces(i,j,each);chessBoard[i][j] = each;each*=-1;}};