封装XMLHTTP类

function JXMLHttp() {
}

JXMLHttp.prototype.instance = null;
JXMLHttp.prototype.context = null;

JXMLHttp.prototype.newInstance = function() {  //创建XMLHTTP对象
   if(this.instance == null) {    
     try {
       return new ActiveXObject("Msxml2.XMLHTTP");
        
     }catch{
      try
      {
        return new ActiveXObject("Microsoft.XMLHTTP");
      }catch{
      }
     }
   }
   return null;
  }
  return this.instance;
}

JXMLHttp.prototype.stop = function() { //停止XMLHTTP运行
  if(this.instance != null) {
   this.instance.abort();
  }
}

JXMLHttp.prototype.request = function(url, data, callback, context) {
  this.instance = this.newInstance();
  if(this.instance != null) {
    var async = typeof(callback) == "function";
    if(async) {
      this.instance.onreadystatechange = function() {
        if(this.instance.readyState == 4) {
          callback( this.response()); 
        } 
      }
    }
    
    this.instance.open('POST', url, async);
    this.instance.send(data);
    
    if(!async) {
      return this.response(); 
    }
  }
}

JXMLHttp.prototype.anylseResult = function() {  // 分析并返回服务器传给客户端数据
  if( (this.instance.responseXML != null) && !(this.instance.responseXML.xml.toString().isNullOrEmpty()) )
    return this.instance.responseXML;
  
  var returnVal = null;
  eval("returnVal=" + this.instance.responseText + ";" );
  return returnVal;
}

JXMLHttp.prototype.response = function() {  //
  if(this.instance != null) {
    var error = "";
    var retValue = "";
    if(this.instance.status == 200) {
      try
      {
        return this.anylseResult();
      }catch
      {
      } 
    } 
  }
  return "";
}