(js) httpRequest with callback

gistfile1.js

 var $ = {
     core:function(u){
       return new $.httpRequest(u);
     },
     httpRequest:function(url, callback){
       var r = new XMLHttpRequest(); 
           r.open("GET", url, true);
           r.onreadystatechange = function () {
             if (r.readyState != 4 || r.status != 200) return; 
             callback(r.responseText);
           };
           r.send();
   }

};

// Use:
$.httpRequest("http://examplesite.com/myurl", function(data) {
   // callback
});