学步园

function makeRequest(url) {
httpRequest = false;
if (window.XMLHttpRequest) {
httpRequest = new XMLHttpRequest();
if (httpRequest.overrideMimeType){
   httpRequest.overrideMimeType('text/xml');
}
} else if (window.ActiveXObject) {
try{
   httpRequest = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
   try {
    httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
   } catch (e) {
   }
}
}
if (!httpRequest) {
alert("您的浏览器不支持当前操作，请使用 IE 5.0 以上版本!");
return false;
}

httpRequest.onreadystatechange = callBack;
httpRequest.open('GET', url, true);

//禁止IE缓存
httpRequest.setRequestHeader("If-Modified-Since","0");

//发送数据
httpRequest.send(null);

//每1秒读取一次后台数据
setTimeout("makeRequest('"+url+"')", 1000);
}

function callBack() {
if (httpRequest.readyState == 4) {
if (httpRequest.status == 0 || httpRequest.status == 200) {
   var result = httpRequest.responseText;
   if(result==""){
    result = "系统取值失败";
   }
   //DOM把结果写入页面
   document.getElementById ("showData").innerHTML="系统获得结果："+result;
} else {//httpRequest.status != 200
   alert("请求失败!");
}
}
}