code: function directionStr(direction) {
      if (direction == DIRECTION_DOWN) {
          return 'down';
      } else if (direction == DIRECTION_UP) {
          return 'up';
      } else if (direction == DIRECTION_LEFT) {
          return 'left';
      } else if (direction == DIRECTION_RIGHT) {
          return 'right';
      }
      return '';
  }
docs: direction cons to string
  @param {Const} direction
  @returns {String}