Simple 2d vector

//2d Vector class (based on Vector.js)
var Vector = function(x,y){ this.x = x || 0; this.y = y || 0; };
Vector.prototype={
	rot: function(a) {
		var theta = a * Math.PI/180,
				cs = Math.cos(theta),
				sn = Math.sin(theta),
				px = this.x * cs - this.y * sn;
				py = this.x * sn + this.y * cs;
		this.x = px;
		this.y = py;
		return this;
	},
	add: function(x,y) { return new Vector(this.x + x, this.y + y); },
	sub: function(x,y) { return new Vector(this.x - x, this.y - y) },
	mul: function(x,y) { return new Vector(this.x * x, this.y * y) },
	neg: function() { return new Vector(-this.x, -this.y);},
	angle: function() { return this.y / this.length();},
	clone: function() { return new Vector(this.x,this.y);},
	dot: function(v)	{ return this.x * v.x + this.y * v.y; },
	len: function() { return Math.sqrt(this.dot(this)) },
	unit: function() { return this.mul(1 / this.len()) },
	angleTo: function(v) { return Math.acos(this.dot(a) / (this.length() * a.length())); }
};