allows using all Jquery AJAX methods in Greasemonkey

GM_XHR.js

// allows using all Jquery AJAX methods in Greasemonkey
// originally inspired from http://ryangreenberg.com/archives/2010/03/greasemonkey_jquery.php
// works with jQuery 2.1.4
// (c) 2011 Martin Monperrus
// (c) 2010 Ryan Greenberg
// (updated) 2015 line0 to work with current jQuery and more closely mirror contemporary XHR implementations.
//
// Usage:
//   $.ajax({
//     url: '/p/',
//     xhr: function(){return new GM_XHR();},
//     type: 'POST',
//     success: function(val){
//        ....
//     }
//   });
(function(window) {
  'use strict';
  
  var GM_XHR = function() {
    GM_XHR.UNSENT = 0;
    GM_XHR.OPENED = 1;
    GM_XHR.HEADERS_RECEIVED = 2;
    GM_XHR.LOADING = 3;
    GM_XHR.DONE = 4;
    
    if (!new.target)
      return GM_XHR;
  
    var xhrRequestDetails = {headers: {}}
    var abortCb = null;
    var events = { onloadstart: null, onprogress: null, onabort: null, onerror: null, onload: null, ontimeout: null, onloadend: null };
  
    // XHR attributes
    this.status = 0;
    this.statusText = '';
    this.readyState = GM_XHR.UNSENT;
    this.timeout = 0;
    this.withCredentials = false;
    this.responseURL = '';
    this.responseType = '';
    this.response = '';
    this.upload = Object.assign({}, events);
    this.onreadystatechange = null;
    
    // Event attributes
    Object.assign(this, events);
    
    // Additional GM_XHR attributes
    this.responseHeaders = '';
    
    // XHR methods
    this.abort = function() {
      if (this.readyState == GM_XHR.UNSENT || this.readyState == GM_XHR.DONE) {
        this.readyState = GM_XHR.UNSENT;
      } else abortCb();
    };
  
    this.getAllResponseHeaders = function(name) {
      return this.responseHeaders;
    };
  
    this.getResponseHeader = function(name) {
      console.log(this.responseHeaders)
      var regexp = new RegExp('^'+name+': (.*)$','im');
      var match = regexp.exec(this.responseHeaders);
      if (match) { return match[1]; }
      return null;
    };
  
    this.overrideMimeType = function(mime) {
      if(this.readyState == GM_XHR.LOADING || this.readyState == GM_XHR.DONE)
        throw new Error("Can't override mime type, request already loading or done.");
      xhrRequestDetails.overrideMimeType = mime;
    };
  
    this.open = function(method, url, _async = true, user = null, password = null) {
      if (!_async)
        throw new Error("Synchronous XHR is no longer supported.");
  
      Object.assign(xhrRequestDetails, {method: method, url: url, user: user, password: password});
      this.readyState = GM_XHR.OPENED;
    };
  
    this.setRequestHeader = function(name, value) {
      xhrRequestDetails.headers[name] = value;
    };
  
    var handleGMXHREvent = (details, handler) => {
      Object.assign(this, details);
      if (handler)
        handler();
    }
    
    this.send = data => {
      let xhr = this;
      abortCb = GM_xmlhttpRequest(Object.assign(xhrRequestDetails, {
        data: data,
        withCredentials: xhr.withCredentials,
        onreadystatechange: details => {
          handleGMXHREvent(details, xhr.onreadystatechange);
          if (false) console.log(`XHR State change:
            state: ${details.readyState}
            status: ${details.statusText} (${details.status})
            response: ${details.responseText}
          `);
        },
        onabort: d => handleGMXHREvent(d, xhr.onabort),
        onerror: d => handleGMXHREvent(d, xhr.onerror),
        onload: d => handleGMXHREvent(d, xhr.onload),
        onprogress: d => handleGMXHREvent(d, xhr.onprogress),
        ontimeout: d => handleGMXHREvent(d, xhr.ontimeout)
      })).abort;
    };
  };
  window.GM_XHR = GM_XHR();
})(window);