Zombie.js - Test if object property found

Im a bit new of Zombie.js testing, and hard to search so I will ask here ...

Example : (Globla variable)

hello = {"world" : "...."}

So I test something like :

describe('Check varibles', function() {
    it('If ---> hello <--- exits', function(done) {
        browser.assert.global('hello');
        done();
    });

    it('If ---> hello.world <--- exits', function(done) {
        // ????
        done();
    });
});

I can check if hello is exits. But how to check if hello.world` is exits ?

I tried with :

browser.assert.global('hello.world'); // AssertionError: undefined == true