Javascript static variables

Something I find strange about Javascript;

[code lang=”javascript”]
function Foo(){};
Foo.prototype = {

bar: [], // or ‘new Array()’ or ‘new Object()’

set: function(val) {
this.bar.push(val);
},

displayBar: function() {
alert (this.bar);
}
}

var foo = new Foo();
foo.set(1);
foo.set(2);

// Alert displays 1,2
foo.displayBar();

// Destoy the object
foo = null;

// Create a new one…
var x = new Foo();

// What does this display?
x.displayBar();
[/code]

By declaring the bar property to be an Array, it seems to make it static to values assigned to the array are in effect updating the class definition - later objects inherit those values. The same works for Objects and both Moz and IE behave the same way, so this would seem to be a feature. The only way to really free the memory is to modify the prototype e.g. Foo.prototype.bar = null;

Anyway haven’t seen it discussed before before - perhaps a useful feature or otherwise a path to eat up memory and forget to free it.