XMLHttpRequest中的ajax是怎样的

本篇文章为大家展示了XMLHttpRequest中的ajax是怎样的，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。

调用

function(Url) {  var XML = new XMLHttpRequest();  XML.onreadystatechange = function() {    if (XML.readyState == 4)    {      if (XML.status == 200)      {        //XML.responseText      }      else      {        //XML.statusText      }    }    else    {      //数据加载中...    }  };  XML.open("GET",Url);  XML.send(null);};

定义XMLHttpRequest 适应不同的浏览器

// IE supportif (window.ActiveXObject && !window.XMLHttpRequest){  window.XMLHttpRequest = function()    {      var msxmls = new Array('Msxml2.XMLHTTP.5.0','Msxml2.XMLHTTP.4.0','Msxml2.XMLHTTP.3.0','Msxml2.XMLHTTP','Microsoft.XMLHTTP');      for (var i = 0; i < msxmls.length; i++)      {        try         {          return new ActiveXObject(msxmls[i]);        }         catch (e)        {        }      }      return null;    };}

// Opera supportif (window.opera && !window.XMLHttpRequest){  window.XMLHttpRequest = function()  {    this.readyState = 0; // 0=uninitialized,1=loading,2=loaded,3=interactive,4=complete    this.status = 0; // HTTP status codes    this.statusText = '';    this._headers = [];    this._aborted = false;    this._async = true;    this._defaultCharset = 'ISO-8859-1';    this._getCharset = function()     {      var charset = _defaultCharset;      var contentType = this.getResponseHeader('Content-type').toUpperCase();      val = contentType.indexOf('CHARSET=');      if (val != -1)       {        charset = contentType.substring(val);      }      val = charset.indexOf(';');      if (val != -1)      {        charset = charset.substring(0, val);      }      val = charset.indexOf(',');      if (val != -1)      {        charset = charset.substring(0, val);      }      return charset;    };    this.abort = function()    {      this._aborted = true;    };    this.getAllResponseHeaders = function()    {      return this.getAllResponseHeader('*');    };    this.getAllResponseHeader = function(header)    {      var ret = '';      for (var i = 0; i < this._headers.length; i++)      {        if (header == '*' || this._headers[i].h == header)        {          ret += this._headers[i].h + ': ' + this._headers[i].v + '\n';        }      }      return ret;    };    this.getResponseHeader = function(header)    {      var ret = getAllResponseHeader(header);      var i = ret.indexOf('\n');      if (i != -1)      {        ret = ret.substring(0, i);      }      return ret;    };    this.setRequestHeader = function(header, value)    {      this._headers[this._headers.length] = {h:header, v:value};    };    this.open = function(method, url, async, user, password)    {      this.method = method;      this.url = url;      this._async = true;      this._aborted = false;      this._headers = [];      if (arguments.length >= 3)       {        this._async = async;      }      if (arguments.length > 3)       {        opera.postError('XMLHttpRequest.open() - user/password not supported');      }      this.readyState = 1;      if (this.onreadystatechange)      {        this.onreadystatechange();      }    };    this.send = function(data)    {      if (!navigator.javaEnabled())      {        alert("XMLHttpRequest.send() - Java must be installed and enabled.");        return;      }      if (this._async)      {        setTimeout(this._sendasync, 0, this, data);      }       else      {        this._sendsync(data);      }    };    this._sendasync = function(req, data)    {      if (!req._aborted)      {        req._sendsync(data);      }    };    this._sendsync = function(data)    {      this.readyState = 2;      if (this.onreadystatechange)      {        this.onreadystatechange();      }      var url = new java.net.URL(new java.net.URL_(window.location.href), this.url);      var conn = url.openConnection();      for (var i = 0; i < this._headers.length; i++)      {        conn.setRequestProperty(this._headers[i].h, this._headers[i].v);      }      this._headers = [];      if (this.method == 'POST')      {

      // POST data        conn.setDoOutput(true);        var wr = new java.io.OutputStreamWriter(conn.getOutputStream(), this._getCharset());        wr.write(data);        wr.flush();        wr.close();      }      // read response headers      // NOTE: the getHeaderField() methods always return nulls for me :(      var gotContentEncoding = false;      var gotContentLength = false;      var gotContentType = false;      var gotDate = false;      var gotExpiration = false;      var gotLastModified = false;      for (var i = 0; ; i++)      {        var hdrName = conn.getHeaderFieldKey(i);        var hdrValue = conn.getHeaderField(i);        if (hdrName == null && hdrValue == null)        {          break;        }        if (hdrName != null)        {          this._headers[this._headers.length] = {h:hdrName, v:hdrValue};          switch (hdrName.toLowerCase())          {            case 'content-encoding': gotContentEncoding = true; break;            case 'content-length' : gotContentLength = true; break;            case 'content-type' : gotContentType = true; break;            case 'date' : gotDate = true; break;            case 'expires' : gotExpiration = true; break;            case 'last-modified' : gotLastModified = true; break;          }        }      }

      // try to fill in any missing header information      var val;      val = conn.getContentEncoding();      if (val != null && !gotContentEncoding) this._headers[this._headers.length] = {h:'Content-encoding', v:val};      val = conn.getContentLength();      if (val != -1 && !gotContentLength) this._headers[this._headers.length] = {h:'Content-length', v:val};      val = conn.getContentType();      if (val != null && !gotContentType) this._headers[this._headers.length] = {h:'Content-type', v:val};      val = conn.getDate();      if (val != 0 && !gotDate) this._headers[this._headers.length] = {h:'Date', v:(new Date(val)).toUTCString()};      val = conn.getExpiration();      if (val != 0 && !gotExpiration) this._headers[this._headers.length] = {h:'Expires', v:(new Date(val)).toUTCString()};      val = conn.getLastModified();      if (val != 0 && !gotLastModified) this._headers[this._headers.length] = {h:'Last-modified', v:(new Date(val)).toUTCString()};      // read response data      var reqdata = '';      var stream = conn.getInputStream();      if (stream)      {        var reader = new java.io.BufferedReader(new java.io.InputStreamReader(stream, this._getCharset()));        var line;        while ((line = reader.readLine()) != null)        {          if (this.readyState == 2)          {            this.readyState = 3;            if (this.onreadystatechange)            {              this.onreadystatechange();            }          }          reqdata += line + '\n';        }        reader.close();        this.status = 200;        this.statusText = 'OK';        this.responseText = reqdata;        this.readyState = 4;        if (this.onreadystatechange)        {          this.onreadystatechange();        }        if (this.onload)        {          this.onload();        }      }      else      {        // error        this.status = 404;        this.statusText = 'Not Found';        this.responseText = '';        this.readyState = 4;        if (this.onreadystatechange)        {          this.onreadystatechange();        }        if (this.onerror)        {          this.onerror();        }      }    };  };}

// ActiveXObject emulation

if (!window.ActiveXObject && window.XMLHttpRequest){  window.ActiveXObject = function(type)  {    switch (type.toLowerCase())    {      case 'microsoft.xmlhttp':        case 'msxml2.xmlhttp':        case 'msxml2.xmlhttp.3.0':        case 'msxml2.xmlhttp.4.0':        case 'msxml2.xmlhttp.5.0':        return new XMLHttpRequest();    }    return null;  };}

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