Source
Gauge(this.bitmapData, [this.direction = DIRECTION_LEFT]) {
var validDirection = false;
validDirection = validDirection || direction == DIRECTION_UP;
validDirection = validDirection || direction == DIRECTION_DOWN;
validDirection = validDirection || direction == DIRECTION_LEFT;
validDirection = validDirection || direction == DIRECTION_RIGHT;
if (!validDirection) throw new ArgumentError('Invalid Gauge direction!');
}