Why does this turn up null instead of being set to the data returned from the ajax call? It must be something simple i am overlooking.

var message;

$(document).ready(function(){
    fbFetchMessage();
    alert(message);
});

function fbFetchMessage(){
    var url = "http://graph.facebook.com/companyname/feed?callback=?";  
        $.getJSON(url,function(json){
            message = json.data[0].message;
        });
}