如何通过微信的的二维码登录原理js代码？

(function($, _aoWin) {

 _aoWin.QRLogin = {};
 _aoWin.LoginLog = "";
 var _sBaseHost = "",
  _oLoginQrCodeImg = document.getElementById("loginQrCode");
 if (document.domain == "qq.com") {
 _sBaseHost = "weixin.qq.com";
 } else if(location.hostname.match(/(wechat\.com)$/)){
 _sBaseHost = "wechat.com";
 }else{
  _sBaseHost = "wechatapp.com";
 }

 var show_tip = 1,
 _sCurUUId,
 _oResetTimeout,
  _aWebMMCallbacks = [],
  _oDetactWebMMInterval = setInterval(function(){
   if(_aoWin.WebMM){
    clearInterval(_oDetactWebMMInterval);
    var callback;
    while(callback = _aWebMMCallbacks.shift()){
     if(typeof(callback) != "function") continue;
     callback();
    }
   }
  }, 1000);

 function _logInPage(_asLog){
  _aoWin.LoginLog = LoginLog + _asLog + "\n";
 }

 function _afterLoadWebMMDo(callback){
  if(!_aoWin.WebMM){
   _aWebMMCallbacks.push(callback);
  }else{
   callback();
  }
 }

 function _reportNow(text){
  _logInPage(text);
  _afterLoadWebMMDo(function(){
   WebMM.ossLog({Text: text});
   WebMM.flushOssLog();
  });
 }

 var reLoadQRImgCount = 0,
  loadQRCodeTime = 0,
  loadQRImgSucc = function(){
   clearInterval(loadQRImgWatchDog);
   _logInPage("Load QRCode Success, time=" + (new Date().getTime() - loadQRCodeTime) + "ms, reload count: " + reLoadQRImgCount);
  },
  loadQRImgFail = function(img){
   _reportNow("Load QRcode fail!" + status + ", src: " + img.src + ", time: " + (new Date().getTime() - loadQRCodeTime) + "ms");
  },
  loadQRImgWatchDog = null;
 function _loadQRImg(uuid) {
  _poll(uuid);
  _logInPage("Load QRCode Start");
  loadQRCodeTime = new Date().getTime();

  _oLoginQrCodeImg.onload = function(){
   loadQRImgSucc();
   _oLoginQrCodeImg.onload = null;
  };
  _oLoginQrCodeImg.onerror = function(){loadQRImgFail(this)};
  _oLoginQrCodeImg.src = "https://login."+_sBaseHost+"/qrcode/"+uuid+"?t=webwx";

  loadQRImgWatchDog = setInterval(function(){
   if (reLoadQRImgCount >= 5) {
    _reset();
    return;
   }
   reLoadQRImgCount++;

   var _img = new Image();
   _img.onload = function () {
    if(!_oLoginQrCodeImg.onload) return;

    _oLoginQrCodeImg.onload = null;
    _oLoginQrCodeImg.src = this.src;//replace
    loadQRImgSucc();
   };
   _img.onerror = function(){loadQRImgFail(this)};
   _img.src = _oLoginQrCodeImg.src + "&r=" + new Date().getTime();
  }, 5000);
 }

 var _sSecondRequestTime = 0,
  _nAjaxTimeout = 100 * 1000,
  _nNewLoginFuncErrCount = 0;
 function _poll(_asUUID) {
 var _self = arguments.callee,
   _nTime = 0;
 _sCurUUId = _asUUID;

  _logInPage("_poll Request Start, time: " + new Date().getTime());
  _nTime = new Date().getTime();
 $.ajax({
 type: "GET",
 url: "https://login." + _sBaseHost + "/cgi-bin/mmwebwx-bin/login?uuid=" + _asUUID + "&tip=" + show_tip,
 dataType: "script",
 cache: false,
 timeout: _nAjaxTimeout,
 success: function(data, textStatus, jqXHR) {
   _logInPage("_poll Request Success, code: " + window.code + ", time: " + (new Date().getTime() - _nTime) + "ms");
 switch (_aoWin.code) {
 case 200:
    _sSecondRequestTime = new Date().getTime() - _sSecondRequestTime;
    _logInPage("Second Request Success, time: " + _sSecondRequestTime + "ms");
 clearTimeout(_oResetTimeout);

    var _fNewLoginFunc = function(){
     $.ajax({
      url: _aoWin.redirect_uri + "&fun=new",//new login page
      type: "GET",
      success:function(msg) {
       _logInPage("new func reponse, reponseMsg: " + msg);
       var code = msg.match(/<script>(.*)<\/script>/);
       var skey=msg.match(/<skey>(.*)<\/skey>/);
       if(code){
        eval(code[1]);
       }else{
        $("#container").show();
        $("#login_container").hide();
       }
       if(skey && skey[1]){
        WebMM.model("account").setSkey(skey[1]);
       }
      },
      error:function(jqXHR, textStatus, errorThrown){
       _nNewLoginFuncErrCount++;
       if(_nNewLoginFuncErrCount > 5){
        if(confirm("Call new login page func error, refresh?")){location.reload()}
        return;
       }
       _reportNow(_aoWin.redirect_uri + " New login page func error: " + textStatus +" retryCount:" + _nNewLoginFuncErrCount);
       setTimeout(_fNewLoginFunc, 500);
      }
     });
    };
    _fNewLoginFunc();

    _reportNow("/cgi-bin/mmwebwx-bin/login, Second Request Success, uuid: " + _asUUID + ", time: " + _sSecondRequestTime + "ms");
 break;

 case 201:
    clearTimeout(_oResetTimeout);
 show_tip = 0;
 $('.errorMsg').hide();
 $('.normlDesc').hide();
 $('.successMsg').show();
    _reportNow("/cgi-bin/mmwebwx-bin/login, First Request Success, uuid: " + _asUUID);
    _reportNow("/cgi-bin/mmwebwx-bin/login, Second Request Start, uuid: " + _asUUID);

    _sSecondRequestTime = new Date().getTime();

    //_nAjaxTimeout = 5 * 1000;
    _self(_asUUID);
    break;

 case 408:
 setTimeout(function(){
  _self(_asUUID);
 }, 500);
 break;

 case 400:
 case 500:
    _reset();
    _afterLoadWebMMDo(function(){
  _aoWin.Log.d("500, Login Poll Svr Exception");
 });
 break;
 }
 },
 error: function(jqXHR, textStatus, errorThrown) {
 if (textStatus == 'timeout') {
    setTimeout(function(){
     _self(_asUUID);
    }, 500);
 } else {
    setTimeout(function(){
     _self(_asUUID);
    }, 5000);

    _logInPage("_poll Request Error:" + textStatus);
    _afterLoadWebMMDo(function(){
     _aoWin.Log.e("Login Poll Error:" + textStatus);
    });
 }
 }
 });
 }

 var getUUIDCount = 0,
  _getUUIDWatchDog,
  _bGetUUIDSuccess = false;//ajax successִ
 function _getUUID() {
  getUUIDCount++;
  var _self = arguments.callee,
   _loadError = function(errorText){
    _reportNow("Load UUID Error! ErrorText: " + errorText + " getUUIDCount=" + getUUIDCount);
    if(getUUIDCount > 5){
     if (confirm("Load uuid error. Refresh?")) {
      location.reload();
     }
    }
    setTimeout(function(){
     _self();
    }, 500);
   };

  clearTimeout(_getUUIDWatchDog);
  _getUUIDWatchDog = setTimeout(function(){
   if(!_aoWin.QRLogin.code){
    _logInPage("GetUUID Timeout, WatchDog Run");
    _self();
   }
  }, 10000);

  $.ajax({
   type: "GET",
   url: "https://login." + _sBaseHost + "/jslogin?appid=wx782c26e4c19acffb&redirect_uri="+encodeURIComponent(location.protocol+"//"+location.host+"/cgi-bin/mmwebwx-bin/webwxnewloginpage")+"&fun=new&lang=" + document.lang,
   dataType: "script",
   cache: false,
   success : function(){
    clearTimeout(_getUUIDWatchDog);
    if(_bGetUUIDSuccess) return;
    if (_aoWin.QRLogin && _aoWin.QRLogin.code == 200) {
     _logInPage("GetUUID Success, UUID=" + QRLogin.uuid);
     _bGetUUIDSuccess = true;

     clearTimeout(_oResetTimeout);
     _oResetTimeout = setTimeout(function(){
      location.reload();//Note: Don't run _reset(). If you run _reset(), there will may have many _poll request, as they get 408 return code
     }, 5 * 60 *1000);//5 mins

     _loadQRImg(QRLogin.uuid);
    } else {
     var QRLoginCode = (_aoWin.QRLogin && _aoWin.QRLogin.code) ? _aoWin.QRLogin.code : "None";
     _logInPage("GetUUID Error, QRLogin.code=" + QRLoginCode);
     _loadError("QRLogin.code= " + QRLoginCode);
    }
   },
   error : function(xhr, textStatus, errorThrown){
    _logInPage("GetUUID Error, textStatus=" + textStatus);
    _loadError(textStatus);
   }
  });
 }

 function _reset(){
  location.reload();
 }

 if ($("#login_container").is(":visible") ) {
  _getUUID();
 }

 
 var _bHadLog = false;
 function _ossLog() {
 if (_bHadLog) return;
 _bHadLog = true;
 var _sUvid = document.cookie.match(new RegExp( "(^| )"+"webwxuvid"+"=([^;]*)(;|$)"));
  if(!_sUvid || _sUvid.length < 3) return;
  _sUvid = _sUvid[2];
 (new Image()).src = "/cgi-bin/mmwebwx-bin/webwxstatreport?funkey=indexdemo&uvid="+_sUvid+"&uuid="+_sCurUUId;
 }


 if($("img.guide").length > 0) {
 var _nTimer = 0,
 _oGuide$ = $(".guide"),
 _oGuideTrigger$ = $("#guideTrigger, #tipTrigger"),
 _oMask$ = $(".mask");

 function _back() {
 _nTimer = setTimeout(function() {
 _oMask$.stop().animate({opacity:0}, function(){$(".mask").hide()});
 _oGuide$.stop().animate({marginLeft:"-120px",opacity:0}, "400", "swing",function(){
  _oGuide$.hide();
 });
 }, 100);
 }

 /*guide*/
 _oGuide$.css({"left":"50%", "opacity":0});
 _oGuideTrigger$.css({"backgroundColor":"white", "opacity":"0"});
 _oGuideTrigger$.mouseover(function(){
 clearTimeout(_nTimer);
 _oMask$.show().stop().animate({"opacity":0.2});
 _oGuide$.css("display", "block").stop().animate({marginLeft:"+168px", opacity:1}, 900, "swing", function() {
 _oGuide$.animate({marginLeft:"+153px"}, 300);
 });
 _ossLog();
 }).mouseout(_back);

 _oGuide$.mouseover(function(){
 clearTimeout(_nTimer);
 }).mouseout(_back);
 }
})(jQuery, window);