HTML-XMLHttpRequest

var xhr = null;
if(window.XMLHttpRequest){
    xhr=  new XMLHttpRequest();
}else{
    xhr = new ActiveXObject("Microsoft.XMLHTTP");
}
xhr.open(method,url,true);//true为异步，false为同步
xhr.onreadystatechange=function(){
    if (xhr.readystate == 4){
        if(xhr.status == 200){
            //xhr.responseText/responseXML
        }
    }
}    
xhr.send(null);