<script type="text/javascript">
var maxID = 0;
function showmsg()
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function(){
if(xhr.readyState==4){
eval("var jn_info="+xhr.responseText);
var s = "";
for(var i=0; i < jn_info.length; i++){
s += '<p>'+jn_info[i].jieshuo+" :"+jn_info[i].content+"</p>";
maxID = info[i].id;
}
var hm =document.getElementById('show_msg');
hm.innerHTML += s;
hm.scrollTop = hm.scrollHeight;
}
}
xhr.open('get','./jieshuo_data.php?maxID='+maxID);
xhr.send(null);
}

 window.onload = function(){
            setInterval("showmsg()",2000);
        }
</script>

//处理页面
$maxID = $_GET['maxID'];

$sql = "select * from jieshuo where id>".$maxID;
$rs=mysqli_query($conn,$sql);
$info = array();
while($row= mysqli_fetch_assoc($rs)){
$info[] = $row;
}

echo json_encode($info);

{

兄弟，你还是把代码格式化下，然后我在帮你看看，你这个看的头疼

<script type="text/javascript">
var maxID = 0;
function showmsg()
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function(){
if(xhr.readyState==4){
eval("var jn_info="+xhr.responseText);
var s = "";
for(var i=0; i < jn_info.length; i++){
s += '<p>'+jn_info[i].jieshuo+" :"+jn_info[i].content+"</p>";
maxID = info[i].id;    //没看懂这句有何意义，你也没有比较最大id啊，还有maxID = info[i].id;     这个你是不是调用错了？哪来的info，不是jn_info吗？
}
var hm =document.getElementById('show_msg');
hm.innerHTML += s;
hm.scrollTop = hm.scrollHeight;
}
}
xhr.open('get','./jieshuo_data.php?maxID='+maxID);
xhr.send(null);
}

 window.onload = function(){
            setInterval("showmsg()",2000);
        }
</script>

为什么不用jQuery里的ajax呢

你好 ，这段代码换掉： 记得 导入 jq 希望采纳

<script type="text/javascript">
var maxID = 0;
function showmsg()
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function(){
if(xhr.readyState==4){
eval("var jn_info="+xhr.responseText);
var s = "";
for(var i=0; i < jn_info.length; i++){
s += '<p>'+jn_info[i].jieshuo+" :"+jn_info[i].content+"</p>";
maxID = info[i].id;
}
var hm =document.getElementById('show_msg');
hm.innerHTML += s;
hm.scrollTop = hm.scrollHeight;
}
}
xhr.open('get','./jieshuo_data.php?maxID='+maxID);
xhr.send(null);
}

 window.onload = function(){
            setInterval("showmsg()",2000);
        }
</script>

///=换成下面的=============================================

<script type="text/javascript">
      var maxID = 0;
    function showmsg(){
        $.ajax({
            url: "./jieshuo_data.php",
            type: 'get',
            data: {
                maxID:maxID
            },
            dataType: 'JSON',
            timeOut: 3000,
            success: function (data) {
                console.log(data)

                // for(var i=0; i < data.length; i++){
                //     s += '<p>'+data[i].jieshuo+" :"+data[i].content+"</p>";
                //     maxID = data[i].id;
                // }
                // var hm =document.getElementById('show_msg');
                // hm.innerHTML += s;
                // hm.scrollTop = hm.scrollHeight;
            }

        })

    }
</script>