#### Vector 2

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```/**
* In mathematics and physics, a vector is an element of a vector space.
*
* The Vector2-class implements 2-dimensional vectors together with various vector-operations.
* @see https://en.wikipedia.org/wiki/Vector_(mathematics_and_physics).
*/

class Vector2 {
constructor (x, y) {
this.x = x
this.y = y
}

/**
* Check for exact vector equality.
*
* @param vector The vector to compare to.
* @returns Whether they are exactly equal or not.
*/
equalsExactly (vector) {
return this.x === vector.x && this.y === vector.y
}

/**
* Check for approximate vector equality.
*
* @param vector The vector to compare to.
* @param epsilon The allowed discrepancy for the x-values and the y-values.
* @returns Whether they are approximately equal or not.
*/
equalsApproximately (vector, epsilon) {
return (Math.abs(this.x - vector.x) < epsilon && Math.abs(this.y - vector.y) < epsilon)
}

/**
* Vector length.
*
* @returns The length of the vector.
*/
length () {
return Math.sqrt(this.x * this.x + this.y * this.y)
}

/**
* Normalization sets the vector to length 1 while maintaining its direction.
*
* @returns The normalized vector.
*/
normalize () {
const length = this.length()
if (length === 0) {
throw new Error('Cannot normalize vectors of length 0')
}
return new Vector2(this.x / length, this.y / length)
}

/**
*
* @param vector The vector to be added.
* @returns The sum-vector.
*/
const x = this.x + vector.x
const y = this.y + vector.y
return new Vector2(x, y)
}

/**
* Vector subtraction
*
* @param vector The vector to be subtracted.
* @returns The difference-vector.
*/
subtract (vector) {
const x = this.x - vector.x
const y = this.y - vector.y
return new Vector2(x, y)
}

/**
* Vector scalar multiplication
*
* @param scalar The factor by which to multiply the vector.
* @returns The scaled vector.
*/
multiply (scalar) {
const x = this.x * scalar
const y = this.y * scalar
return new Vector2(x, y)
}

/**
* Distance between this vector and another vector.
*
* @param vector The vector to which to calculate the distance.
* @returns The distance.
*/
distance (vector) {
const difference = vector.subtract(this)
return difference.length()
}

/**
* Vector dot product
*
* @param vector The vector used for the multiplication.
* @returns The resulting dot product.
*/
dotProduct (vector) {
return this.x * vector.x + this.y * vector.y
}

/**
* Vector rotation (see https://en.wikipedia.org/wiki/Rotation_matrix)
*
* @param angleInRadians The angle in radians by which to rotate the vector.
* @returns The rotated vector.
*/
const x = ca * this.x - sa * this.y
const y = sa * this.x + ca * this.y
return new Vector2(x, y)
}

/**
* Measure angle between two vectors
*
* @param vector The 2nd vector for the measurement.
* @returns The angle in radians.
*/
angleBetween (vector) {
return Math.atan2(vector.y, vector.x) - Math.atan2(this.y, this.x)
}
}

export { Vector2 }
```  