Vector. Verlet, and Linear Constraints in javascript (so I don't have to write a new one every week... :P)

Verlet.js

function Vector(x,y){
	this.x = x;
	this.y = y;
};
Vector.prototype.iadd = function(x, y){
	if(typeof(x)=="number"){
		this.x += x;
		this.y += y;
	}else{
		this.x += x.x;
		this.y += x.y;
	}
	return this;
};
Vector.prototype.isub = function(x, y){
	if(typeof(x)=="number"){
		this.x -= x;
		this.y -= y;
	}else{
		this.x -= x.x;
		this.y -= x.y;
	}
	return this;
};
Vector.prototype.imul = function(x, y){
	if(typeof(x)=="number"){
		this.x *= x;
		this.y *= y;
	}else{
		this.x *= x.x;
		this.y *= x.y;
	}
	return this;
};
Vector.prototype.idiv = function(x, y){
	if(typeof(x)=="number"){
		this.x /= x;
		this.y /= y;
	}else{
		this.x /= x.x;
		this.y /= x.y;
	}
	return this;
};
Vector.prototype.add = function(x, y){
	var temp = new Vector(this.x, this.y);
	return temp.iadd(x, y);
};
Vector.prototype.sub = function(x, y){
	var temp = new Vector(this.x, this.y);
	return temp.isub(x, y);
};
Vector.prototype.mul = function(x, y){
	var temp = new Vector(this.x, this.y);
	return temp.imul(x, y);
};
Vector.prototype.div = function(x, y){
	var temp = new Vector(this.x, this.y);
	return temp.idiv(x, y);
};
Vector.prototype.set = function(x, y){
	if(typeof(x)=="number"){
		this.x = x;
		this.y = y;
	}else{
		this.x = x.x;
		this.y = x.y;
	}
};
Vector.prototype.norm = function(){
	return Math.sqrt(this.x * this.x + this.y * this.y);
};
var Verlet = function(){
	Vector.apply(this, arguments);
	this.previous = new Vector(this.x, this.y);
};

Verlet.prototype = Vector.prototype;
Verlet.prototype.step = function(){
	var temp = this.sub(this.previous);
	this.previous.set(this);
	this.iadd(temp);
};

var Constraint = function(a,b,width){
	this.a = a;
	this.b = b;
	this.width = width;
};
Constraint.prototype.constrain = function(){
	var d1 = this.a.sub(this.b);
	var d2 = d1.norm();
	var d3 = (this.width - d2)/d2;
	var d4 = d1.mul(d3*0.5, d3*0.5);
	this.a.iadd(d4);
	this.b.isub(d4);
};