var XMLHTTPRequest = (function(){

  var xhr = function (opt) {
    this.status = 0
    this.readyState = 0
    this.response = ""
    this.responseText = ""
    this.responseType = "" // "" arraybuffer blob document json text
    this.responseXML = ""
    this.statusText = ""
    this.timeout = 0
    this.onreadystatechange = function(){}
    this.ontimeout = function(){}
    this.onload = function(){}
    this.headers = []
    this.upload = {}
    this.withCredentials = false
  }
  xhr.prototype.open = function(method, url, async, user, password){
  }
  xhr.prototype.abort = function(){
  }
  xhr.prototype.getAllResponseHeaders = function(){
  }
  xhr.prototype.getResponseHeader = function(){
  }
  xhr.prototype.overrideMimeType = function(){
  }
  xhr.prototype.setRequestHeader = function(key, value){
    this.headers.push({ key: key, value: value })
  }
  xhr.prototype.send = function(data){
  }

})()