clockwise(vec) {
    let a = this.y * vec.x;
    let b = this.x * vec.y;

    if (a > b) {
      return -1;
    } else if (a === b) {
      return 0;
    }

    return 1;
  }
Checks whether or not this vector is in a clockwise or counter-clockwise rotational direction compared to another vector in relation to the coordinate system.

@param {Vector2} vec Another vector.
@returns {Number} Returns -1, 0 or 1 if the vector supplied as an argument is clockwise, neutral or counter-clockwise respectively to this vector in relation to the coordinate system.