ajax异步判断网站是否可以访问到的解决方法
function getXMLHttpRequest(){var client = getXMLHttpRequestFromIE(); if(client == null){ client = new XMLHttpRequest(); }return client;}function getXMLHttpRequestFromIE(){var namePrefixes = ["Msxml3","Msxml2","Msxml","Microsoft"];for(var i = 0; i < namePrefixes.length; i++){ try{ var name = namePrefixes + ".XMLHTTP"; return new ActiveXObject(name); }catch(e){ }}return null;}var client = null;//是否可以访问var isRun = false;//返回值var stateString="";//请求url的网站function connUrl(url){client = getXMLHttpRequest();var actionURL = convertURL(url);try{client.open("GET", actionURL, true);client.onreadystatechange = callBack;client.send(null);}catch(e){}finally{}}function callBack(){if(client.readyState == 4){stateString = client.responseText;if(stateString && client.status==200)isRun = true;}}//是否可达function isReach(url){connUrl(url);return isRun;}//给url地址增加时间戳，骗过浏览器，不读取缓存 function convertURL(url) { //获取时间戳 var timstamp = (new Date()).valueOf(); //将时间戳信息拼接到url上 if (url.indexOf("?") >= 0) { url = url + "&t=" + timstamp; } else { url = url + "?t=" + timstamp; } return url; }//因为是异步，先调用，此时isRun的值是falseisReach("http://www.baidu.com");//3秒钟后判断isRun的值，如果为false认为网站不可达，类似超时时间setTimeout(function(){ //alert(stateString); //alert(isRun);if(isRun==true){document.getElementById("ceshi").innerText = "网站是通的！";}else{document.getElementById("ceshi").innerText = "网站不通！";}},3000);<div id="ceshi"></div>
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