Vector2.js

function Vector2(x = 0, y = 0){

    this.x = x;
    this.y = y;
}

Vector2.prototype.copy = function(){
    return new Vector2(this.x, this.y);
}

Vector2.prototype.add = function(vector){
    return new Vector2(this.x + vector.x, this.y + vector.y);
}

Vector2.prototype.addTo = function(vector){
    this.x += vector.x;
    this.y += vector.y;
}

Vector2.prototype.subtract = function(vector){
    return new Vector2(this.x - vector.x, this.y - vector.y);
}

Vector2.prototype.mult = function(scalar){

    return new Vector2(this.x * scalar, this.y * scalar);
}

Vector2.prototype.dot = function(vector){
    return this.x * vector.x + this.y * vector.y;
}

Vector2.prototype.length = function(){
    return Math.sqrt(Math.pow(this.x, 2) + Math.pow(this.y, 2));
}

Vector2.prototype.distFrom = function(vector){
    return this.subtract(vector).length();
}