Intercept Ajax responses and forward them to a separate host

AjaxIntercept.user.js

// ==UserScript==
// @name        AjaxTest
// @namespace   intercept
// @include     <site>
// @version     1
// @grant       GM_xmlhttpRequest
// ==/UserScript==

function main () {
  window.alert = function() {
    return console.log.apply(this, arguments);
  }
  
  window.stash = Array();
  window.XMLHttpRequest.prototype.otherOpen = window.XMLHttpRequest.prototype.open;
  
  window.XMLHttpRequest.prototype.open = function() {
    this.addEventListener("readystatechange", function() {
      if (this.readyState == 4) {
        console.log(this.responseText);
        window.stash.push(this.responseText);
        deliver();
      }
    }, false);
    window.XMLHttpRequest.prototype.otherOpen.apply(this, arguments);
  };
}

var script = document.createElement('script');
script.appendChild(document.createTextNode('('+ main +')();'));
(document.body || document.head || document.documentElement).appendChild(script);

function deliver() {
  console.log('delivering...');
  while (i = unsafeWindow.stash.shift()) {
    console.log('Shifted: [' + i + ']');
    GM_xmlhttpRequest({
      method: "POST",
      url: "endpoint.php",
      headers: {
        "Content-Type": "application/x-www-form-urlencoded"
      },
      data: 'intel=' + JSON.stringify(i),
      onload: function(response) {
        console.log(response.responseText);
      }
    });
  }
}

exportFunction(deliver, unsafeWindow, {defineAs: "deliver"});