gistfile1.js

//Use an object as a set
var set = {}

//Create an object, give it some property
var item = {}
item.Foo = function() {};
set[item] = item;

for (key in set}
{
    key.Foo(); //<-- nope
}

for (key in set)
{
    set[key].Foo(); //<-- just fine
}