Some JS Vector stuff

Vector2D.js

/*jshint curly:false */
/*global define:true */
define(function() {
  "use strict";

  function Vector2D(x,y) {
    Object.defineProperties(this, {
      x: { value: x, enumerable: true },
      y: { value: y, enumerable: true },
      _length: { writable: true } 
    });
  }

  
  function dot(a, b) {
    return (a.x * b.x) + (a.y * b.y);
  }
  
  Vector2D.dot = dot;

  var zero = Vector2D.zero = new Vector2D(0,0);

  // Create a vector from the polar coordinates (r, theta).
  Vector2D.fromPolar = function (radius, angle) {
      return new Vector2D(radius * Math.cos(angle), radius * Math.sin(angle));
  };

  Vector2D.prototype = {
    negate: function () {
      return new Vector2D(-this.x, -this.y);
    },
    add: function (other) {
      return new Vector2D(this.x + other.x, this.y + other.y);
    },
    sub: function (other) {
      return new Vector2D(this.x - other.x, this.y - other.y);
    },
    length: function () {
      var length = this._length;
      if (length !== undefined) return length;
      this._length = length = Math.sqrt(this.lengthSquared);
      return length;
    },
    scale: function (factor) {
      return new Vector2D(this.x * factor, this.y * factor);
    },
    distanceSquared: function (other) {
      var dx = this.x - other.x, dy = this.y - other.y;
      return dx*dx + dy*dy;
    },
    normalize: function () {
      var length = this.length(),
          x = this.x, y = this.y;
      if (length <= 0) return zero;
      return new Vector2D(x / length, y / length);
    },
    toLength: function (scale) {
      var length = this.length();

      if (length <= 0 || scale === 0)
        return zero;
      
      var factor = scale / length,
          x = this.x, y = this.y;
      return new Vector2D(x * factor, y * factor);
    },
    truncatedLength: function(max) {
      var lengthSquared = this.lengthSquared;
      return (lengthSquared <= max * max) ? this : this.normalizedScale(max);
    },
    perpindicular: function () {
      return new Vector2D(-this.y, this.x);
    },
    rotate: function (theta) {
      var x = this.x, y = this.y,
          c = Math.cos(theta), s = Math.sin(theta);
      return new Vector2D(
        (x * c) - (y * s),
        (x * s) + (y * c));
    },
    projectOnto: function (dest) {
      var factor = dot(this, dest) / dest.lengthSquared;
      return dest.scale(factor);
    },
    perpindicularOnto: function (dest) {
      return this.projectOnto(dest.perpindicular());
    }
  };

  Object.defineProperty(Vector2D.prototype, 'lengthSquared', {
    get: function () {
      var x = this.x, y = this.y;
      return x*x + y*y;
    }
  });


  return Vector2D;
});