Trying to get a JSON replacer to detect Ctor type...

replacer_test.js

var Foo = function Foo() {
    this.id = 1;
}

var Bar = function Bar(foo) {
    this.id = 2;
    this.buddies = {};
}

Bar.prototype.toJSON = function() {
    return this.buddies;
}

Bar.prototype.__defineSetter__('foo', function(value) {
    this.buddies['foo'] = value;
});

Bar.prototype.__defineGetter__('foo', function() {
    return this.buddies['foo'];
});

var f = new Foo();

var b = new Bar();

b.foo = f;

function objToId(key, value) {
    console.log(value.constructor);
    if(value.constructor == Foo) {
        return value.id;
    }
    else {
        return value;
    }
}

console.log(JSON.stringify(b, objToId));

So here's the problem.... The above gist works. The issue I'm having is that the same process doesn't work when it's applied to my larger project, and it's driving me nuts.