Simplest cross-browser cross domain XHR ever.

cross.js

var request = function(url, success) {
  if ('XDomainRequest' in window) {
    var xdr = new XDomainRequest();
    xdr.onload = function() {
      alert(xdr.responseText);
      success(JSON.parse(xdr.responseText));
    };
    xdr.open('GET', url);
    xdr.send(null);
  } else {
    var xhr = new XMLHttpRequest();
    xhr.onreadystatechange = function() {
      if (xhr.readyState == 4) {
        success(JSON.parse(xhr.responseText));
      }
    };
    xhr.open('GET', url, true);
    xhr.setRequestHeader('Accept', 'application/json');
    xhr.send(null);
  }
};