chess.js

var WHITE_KING = 100;
var WHITE_QUEEN = 90;
var WHITE_ROOK = 50;
var WHITE_BISHOP = 31;
var WHITE_KNIGHT = 30;
var WHITE_PAWN = 10;

var BLACK_KING = -WHITE_KING;
var BLACK_QUEEN = -WHITE_QUEEN;
var BLACK_ROOK = -WHITE_ROOK;
var BLACK_BISHOP = -WHITE_BISHOP;
var BLACK_KNIGHT = -WHITE_KNIGHT;
var BLACK_PAWN = -WHITE_PAWN;