iPhone does not recognize PhoneGap's navigator.app

I have a button to exit from the application. The function looks like this:

//Close application
function close_window() {
  navigator.app.exitApp();
}

It did not work, so I tried the following line:

navigator.device.exitApp();

It did not work either. Then I discovered by alert that the iPhone does not recognize PhoneGap's navigator.app and navigator.device. I use PhoneGap version 2.2.0.

Why is this happening?

P.S.: It works for me on Android.