$.ajax({ url:url, type:"POST", data:JSON.stringify(data), dataType:"json", contentType:"application/json", success:function(res){ } })
var xhr = new XMLHttpRequest();
xhr.open("POST","www.baidu.com");
xhr.setRequestHeader("Content-Type", "application/json")
xhr.send(JSON.stringify({a:1,data:[1,2,3]}));