Should wrap property of undefined: navigator.app

I am trying to stub navigator.app.loadUrl which I use for redirecting like: navigator.app.loadUrl(www.redirecturl.com, {openExternal: true});

Doing this gives the error:

Should wrap property of object

I am trying to stub this method using: var navigatorStub = sinon.stub(navigator.app, 'loadUrl'); What am I doing wrong?

Stubbing properties of navigator does work. Like navigator.splashscreen