SAPUI5 Logoff event in ApplicationHeader

I am currently working on a SAP XS application. Using the API, I want to log off my user on the website. Im totally new on Javascript soplease dont mind the probable ease of my question.

The API (https://sapui5.hana.ondemand.com/sdk/docs/api/symbols/sap.ui.commons.ApplicationHeader.html#event:logoff) provides the method "fireLogoff". But before that I have to add "attachLogoff" to the applicationheader in my application, right?

My faulty method looks like this:

oAppHeader.attachLogoff(
     function(oControlEvent){
          alert("Logging off...");
          fireLogOff();
     }
);

Thank you a lot for helping me in this matter.