GM_xmlhttpRequest Alert Interference Test

gm_xhr-alert-test.user.js

// ==UserScript==
// @name GM_xmlhttpRequest Alert Interference Test
// @include http*
// ==/UserScript==

// Uses unsafeWindow.dump() because of
//   https://github.com/greasemonkey/greasemonkey/issues#issue/1229

function doSampleXhr() {
  unsafeWindow.dump('starting gm_xhr ...');

  try {

  GM_xmlhttpRequest({
    method: "GET",
    url: "http://localhost/",
    onload: function() { unsafeWindow.dump('gm_xhr loaded\n'); },
    onerror: function() { unsafeWindow.dump('gm_xhr failed\n'); }
  });

  } catch (e) { unsafeWindow.dump(e+'\n'); }

  unsafeWindow.dump(' done\n');
}

var now = (new Date()).valueOf();
var then = parseInt(GM_getValue('last alert', 0), 10);

if (now - then > 60000) {
  alert('Showing an alert which will break GM_xhr\n'
      + '(At URL: '+location.href+')');
  GM_setValue('last alert', String(now));
}
doSampleXhr();