var url = "http://domain/something.jsonp";
var data = {};
var callback = function(data){ alert(data.attribute_name)};

J50Npi.getJSON(url, data, callback);

// This line taken from J50Npi.min.js (within this repo)
var J50Npi={currentScript:null,getJSON:function(b,d,h){var g=b+(b.indexOf("?")+1?"&":"?");var c=document.getElementsByTagName("head")[0];var a=document.createElement("script");var f=[];var e="";this.success=h;d.callback="J50Npi.success";for(e in d){f.push(e+"="+encodeURIComponent(d[e]))}g+=f.join("&");a.type="text/javascript";a.src=g;if(this.currentScript){c.removeChild(currentScript)}c.appendChild(a)},success:null};

// This is a WorldIP free geo-location database.
var url = "http://api.wipmania.com/jsonp";

// No specific data need to be sent there
var data = {};

// We need a function callback to be executed after the response is received
var callback = function(geodata){ alert(geodata.address.country); };

// And here is the magic:
J50Npi.getJSON(url, data, callback);