Jquery Asinchronous Execution context

Jquery Asinchronous Execution context

Hello!

My problem is about passing information inside of "callback on success" function;

Small example:

var myvar = 1;
$.post('www.site.com',data,callbackfunction);
var callbackfunction = function(data){
    alert(myvar);
};

and we got "undefined";

Id like to have something like this:
$.post('www.site.com',data,callbackfunction.bind(document)); //so i can set the execution context


Thank you for any ideas.
I had this feature in prototype framework. Wondering how it is made in jQuery.