Memory

While it works to set default values on the prototype like this, you want to be very careful to not do this with anything you will (or if you ask some people, if you *can*) mutate the values.

```javascript
var Cls = function(){};
Cls.prototype.ary = [];
var instance1 = new Cls();
var instance2 = new Cls();

instance1.ary.push(1);
instance2.ary; // [1]
```

It happens to not be a problem in this case since you're using primitives, but I would probably stick to setting them on the instance within the constructor or an `setDefaults()` method.

/cc @advanced-js/summer-2014