window.location.reload(); reloads page uncontrollably?

can anybody explain why this is? here my code:

<script>
$(document).ready(function()
{
    refresh();
});

function refresh()
{     开发者_运维百科 
    $.getJSON('getMessageDetails.php', function (json) {
        //alert(json.length);
        //$("#subject1").html(json[0].subject);
        //$("#unique_code1").html(json[0].unique_code);  
        $("#msg_id").html(json[0].id);
        $("#subject").html(json[0].subject);
        $("#unique_code").html(json[0].unique_code);  
        if (json.length > 0 )
        {
            //alert(json.length);
            window.location.reload(); 
        }     
        else
        {
            //do something
        } 
    }); 
    window.setTimeout(refresh,30000);
}
</script>

What I am trying to do is if a new message came in json wont be empty so reload the page and if there are no new messages, keep on checking

What happens now is a new message comes in and the screen just starts flashing like crazy! It must do the reload once and then every 30 seconds check again. Any help please? Thank you.

I think you should do:

$(document).ready(function()
{
    var int = setInterval(refresh,30000);
});

function refresh()
{      
$.getJSON('getMessageDetails.php', function (json) {
 //alert(json.length);
 //$("#subject1").html(json[0].subject);
 //$("#unique_code1").html(json[0].unique_code);  
 $("#msg_id").html(json[0].id);
 $("#subject").html(json[0].subject);
 $("#unique_code").html(json[0].unique_code);  
 if (json.length > 0 )
 {
    //alert(json.length);
    window.location.reload(); 
 }     
 else
 {
    //do something
 } 
 }); 

 }

I think you are looking for setInterval instead as it sound like you want to call your function every 30 seconds instead of reloading the whole page (that's what window.location.reloaddoes).

Example:

function sayHello(){
alert('hello once again');
}
setInterval(sayHello,30000);

So what you have to do is wrap your AJAX call in a function and then apply a setInterval that defines when it gets repeated.