AJAX完整示例

var xmlhttp;function createRequest() {if (window.ActiveXObject) {        xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");    }    else if (window.XMLHttpRequest) {        xmlhttp = new XMLHttpRequest();    }}createRequest();function sendRequest(){if(xmlhttp){xmlhttp.open("GET", "URL", true);xmlhttp.send(null);xmlhttp.onreadystatechange = getRequestAndManager;}}function getRequestAndManager(){if (xmlhttp_request.readyState == 4) {// 收到完整的服务器响应if (xmlRequest.status == 200) {var requestReturnStr = xmlhttp.responseText;var json = eval("("+requestReturnStr+")");}} }

跨域请求(跨域端口也属于跨域，80和8080属于跨域)在火狐等标准浏览器中Status为0，而且responseText为""，所以要注意这个问题