Base Vector2 JavaScript math helper class serves methods to perform operations on object values within Cartesian coordinate systems.

Vector2.js

var Vector2 = function () {
  this._x = 0;
  this._y = 0;
  this.DEGRAD = 0;
};

Vector2.prototype.initialize = function (x, y) {
  _x = x;
  _y = y;
};

Vector2.prototype.getX = function () {
  return _x;
};

Vector2.prototype.setX = function (x) {
  _x = x;
};

Vector2.prototype.getY = function () {
  return _y;
};

Vector2.prototype.setY = function (y) {
  _y = y;
};

// ------------------- public methods ------------------- //

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

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

Vector2.prototype.multiply = function (vector) {
  return new Vector2(_x * vector.x, _y * vector.y);
};

Vector2.prototype.divide = function (vector) {
  return new Vector2(_x / vector.x, _y / vector.y);
};

Vector2.prototype.distance = function (vector) {
  var deltaX = _x - vector.x;
  var deltaY = _y - vector.y;
  return Math.sqrt(deltaX * deltaX + deltaY * deltaY);
};

Vector2.prototype.distanceSqr = function (vector) {
  var deltaX = _x - vector.x;
  var deltaY = _y - vector.y;
  return (deltaX * deltaX + deltaY * deltaY);
};

Vector2.prototype.magnitude = function () {
  return Math.sqrt(_x * _x + _y * _y);
};

Vector2.prototype.normalize = function () {
  var mag = Math.sqrt(_x * _x + _y * _y);

  if (mag === 0) {
    _x = 0;
    _y = 0;
  } else {
    _x = _x / mag;
    _y = _y / mag;
  }
};

Vector2.prototype.getNormalized = function () {
  var mag = Matn.sqrt(_x * _x + _y * _y);
  return new Vector2(_x / mag, _y / mag);
};

Vector2.prototype.getAngle = function () {
  return Math.atan2(_y, _x) * 180 / Math.PI;
};

Vector2.prototype.degToVec = function (deg) {
  var rad = deg * DEGRAD;
  return new Vector2(Math.cos(rad), Math.sin(rad));
};

Vector2.prototype.radToVec = function () {
  return new Vector2(Math.sin(rad), Math.cos(rad));
};

// ---------------- additional vector methods ---------------- //

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

Vector2.prototype.rotate = function (deg) {
  var rad = deg * DEGRAD;
  var cos = Math.cos(rad);
  var sin = Math.sin(rad);
  _x = _x * cos - _y * sin;
  _y = _y * cos + _x * sin;
};

Vector2.prototype.perpRight = function () {
  return new Vector2(-_y, _x);
};

Vector2.prototype.toString = function () {
  return ("x : " + int(_x * 100) / 100 + ", \ty : " + int(_y * 100) / 100);
};

this is not good.
like "this._x"

use like this format
contructor() {
local variable;
#define methods
this.getX = ...
}