Js obj with private and public api

/** js object built like a java class with private and public API */
var usernameHandler = ( function() {

    // private api
    var _srvCallbk = function( data ) {
        $('#usernameContainer').html( data.username );
    };

    var _callService = function() {
        _privatefunctionAjaxCall( _srvCallbk );
    };

    var _privatefunctionAjaxCall( callback )  {
        // ... here for example you can do an ajax call to a service
    }

    // public api
    return {
        setUsername: _callService
    }
}());