Access variable's value outside suds.invoke() scope

How can I pass the variable outside the suds.invoke() method. Even Variable is defined globally.I am not able to get value of variable outside the suds.invoke() method while inside its working. i.e

var session ;

suds.invoke('login',logindata, function(xmlDoc) { var xml = this.responseXML; var results = xml.documentElement.getElementsByTagName('return');

        session = results.item(0).text;
        alert (session); // here its working
    });

alert (session); // here its not working I want to access value of session variable outside of suds.invoke() method. Any Quick Best suggestion regarding to this problem.