js中怎么写ajax

var ajaxObj=new XMLHttpRequest();

ajaxObj.open("GET","../php/ajaxSubmitData.php?data=tody is wind");

ajaxObj.send()

ajaxObj.onreadystatechange= function () {

    if(ajaxObj.readyState===4&&ajaxObj.status){

        alert("发送成功");   

    }

}

var ajaxObj=new XMLHttpRequest();

ajaxObj.open("POST","../PHP/ajaxSubmitData.php");

ajaxObj.setRequestHeader("Content-type","application/x-www-form-urlencoded");

// multipart/form-data 默认的以二进制方式传送

ajaxObj.send("data=我是post数据");

ajaxObj.onreadystatechange= function ()

if(ajaxObj.readyState===4&&ajaxObj.status===200){

alert("发送数据成功");

}

}