Inherit parent constructor arguments

One way to do it:

function PhysicsBody( aNode ) {
    this.userData = aNode;
}

PhysicsBody.prototype.pbMethod = function () {};

function DynamicBody( aNode ) {
    PhysicsBody.call( this, aNode );
}

// setting up the inheritance
DynamicBody.prototype = Object.create( PhysicsBody.prototype );

DynamicBody.prototype.dbMethod = function () {};

Now, when you do

var pb = new PhysicsBody( '...' );

the instance pb gets a userData property and also inherits the methods from PhysicsBody.prototype (pbMethod in this case).

When you do

var db = new DynamicBody( '...' );

the instance db gets a userData property and also inherits the methods from DynamicBody.prototype (dbMethod in this case), which in turn inherits from PhysicsBody.prototype.