一份老外写的XMLHttpRequest代码多浏览器支持兼容性

/* 

Cross-Browser XMLHttpRequest v1.2 
================================= 

Emulate Gecko 'XMLHttpRequest()' functionality in IE and Opera. Opera requires 
the Sun Java Runtime Environment <http://www.java.com/>. 

by Andrew Gregory 
http://www.scss.com.au/family/andrew/webdesign/xmlhttprequest/ 

This work is licensed under the Creative Commons Attribution License. To view a 
copy of this license, visit http://creativecommons.org/licenses/by-sa/2.5/ or 
send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 
94305, USA. 

Attribution: Leave my name and web address in this script intact. 

Not Supported in Opera 
---------------------- 
* user/password authentication 
* responseXML data member 

Not Fully Supported in Opera 
---------------------------- 
* async requests 
* abort() 
* getAllResponseHeaders(), getAllResponseHeader(header) 

*/ 
// IE support 
if (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; 
  }; 
} 
// Gecko support 
/* ;-) */ 
// Opera support 
if (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); 
        // this is not really asynchronous and won't execute until the current 
        // execution context ends 
      } 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(); 
      } 
      // open connection 
      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; 
  }; 
}