describe("Angle between", function () {
    var vector, secondVector, angleBetween;
    vector = new Vector(30, 40, 0);
    secondVector = new Vector(-40, 30, 0);
    angleBetween = secondVector.angleBetween(vector);

    it("Result is PI/2", function () {
        expect(angleBetween).toBeCloseTo(Math.PI / 2, 1);
    });
});

angleBetween(pVector) {
    return this.dotProduct(pVector) * Math.cos(0);
}