ajax异步获取数据

function createXHR(){if( typeof XMLHttpRequest != "undefined" ){return new XMLHttpRequest();} else if( typeof ActiveXObject != "undefined" ){var version = ["MSXML2.XMLHttp.6.0","MSXML2.XMLHttp.3.0","MSXML2.XMLHttp"];for( var i = 0; i < version.length; i++ ){try{return new ActiveXObject( version[ i ] );}catch( e ){// 跳过}}}else{throw new Error( "您的浏览器不支持XHR对象！" );}}// 异步 $(function(){$("body").click(function(){var xhr = createXHR();xhr.onreadystatechange = function(){if( xhr.readyState == 4 ){   // 判断是否已经接受到全部响应数据if( xhr.status == 200 ){   // 判断是否返回成功alert( xhr.responseText );}else{throw new Error( "数据返回失败！状态代码：" + xhr.status + ",状态信息是:" + xhr.statusText );}}}xhr.open( "get","demo.php?rand=" + Math.random(),true );xhr.send(null);// xhr.abort();   // 取消异步请求});});