A simple example that polls for new data in a streamed http response.

demo.js

var xhr = function (url, options) {
  options = options || {};
  var req = new XMLHttpRequest(),
      method = options.method || 'get',
      dfd = new $.Deferred();

  req.open(method, url, true);

  req.setRequestHeader('X-Requested-With', 'XMLHttpRequest');

  var last = function (arr) {
    return arr[arr.length - 1];
  };
  req.onreadystatechange = function () {
    if (req.readyState == 3) {
      dfd.notify(last($.trim(req.responseText).split("\n")));
    }
    else if (req.readyState == 4) {
      if ((/^[20]/).test(req.status)) dfd.resolve(req);
      if ((/^[45]/).test(req.status)) req.reject(req);
    }
  };
  req.send();

  return dfd;
};