public void ProcessRequest (HttpContext context) {
    context.Response.ContentType = "text/plain";
    String callbackFunName = context.Request["callbackparam"];
    context.Response.Write(callbackFunName + "([ { name:\"John\"}])");
}

$.ajax({
    type : "get",
    async:false,
    url : "http://www.xxx.com/ajax.do",
    dataType : "jsonp",
    jsonp: "callbackparam",//服务端用于接收callback调用的function名的参数
    jsonpCallback:"success_jsonpCallback",//callback的function名称
    success : function(json){
        alert(json);
        alert(json[0].name);
    },
    error:function(){
        alert(‘fail‘);
    }
});