var http_request = false;

 function send_request(action,url,poststr) {//初始化、指定处理函数、发送请求的函数
  http_request = false;
  //开始初始化XMLHttpRequest对象
  if(window.XMLHttpRequest) { //Mozilla 浏览器
   http_request = new XMLHttpRequest();
   if (http_request.overrideMimeType) {//设置MiME类别
    http_request.overrideMimeType('text/xml');
   }
  }
  else if (window.ActiveXObject) { // IE浏览器
   try {
    http_request = new ActiveXObject("Msxml2.XMLHTTP");
   } catch (e) {
    try {
     http_request = new ActiveXObject("Microsoft.XMLHTTP");
    } catch (e) {}
   }
  }
  if (!http_request) { // 异常，创建对象实例失败
   window.alert("不能创建XMLHttpRequest对象实例.");
   return false;
  }
  http_request.onreadystatechange = processRequest;
  // 确定发送请求的方式和URL以及是否同步执行下段代码
  http_request.open(action, url, true);
  if(action == "POST")
	 http_request.setRequestHeader("Content-Type","application/x-www-form-urlencoded");

  http_request.send(poststr);
 }

	function processRequest() {

  if (http_request.readyState == 4) { // 判断对象状态

    if (http_request.status == 200) { // 信息已经成功返回，开始处理信息

       document.getElementById(currentPos).innerHTML = http_request.responseText;

    } 
	else
	 { //页面不正常

      alert("您所请求的页面有异常。");
   	 }

  }


}