if .get() data same on setInterval do nothing if different reload data - ajax

Question

I have a DIV which is populated from $.get data on doc ready, I then call setInterval every 5 seconds. What im trying to do is on success of the setInterval $.get if the html data for #are_friends is the same as before do nothing but if its different then load the data to #are_friends again.
Does anybody have any idea how I would do this or a better way than Im trying to implement.
<div id="are_friends"></div>
<script type="text/javascript">
$(document).ready(function() {
$.get('<?php echo $siteUrl ?>are_friends.php?userid=<?php echo $userid; ?>', function(data) {
$("#are_friends").html(data);
});
var auto_refresh = setInterval(
function ()
{
$.ajax({
url: "<?php echo $siteUrl ?>are_friends.php?userid=<?php echo $userid; ?>",
success: function(newdata){
var oldcontent = $("#are_friends").html();
if(oldcontent != newdata) {
$("#are_friends").html(newdata);
}
}
});
}, 5000); // refresh every 5000 milliseconds
});
</script>

Answer 1

At least, you could reuse the function getting the data like this:
function getData(callback)
{
$.ajax({
url: "<?php echo $siteUrl ?>are_friends.php?userid=<?php echo $userid; ?>",
success: function(newdata){
callback(newdata);
}
});
}
$(document).ready(function()
{
getData(function(data)
{
$("#are_friends").html(data);
});
var auto_refresh = setInterval(function ()
{
getData(function(newdata)
{
if($("#are_friends").html() != newdata) {
$("#are_friends").html(newdata);
}
});
}, 5000);
});
Practically, the initial call and the subsequent call is the same, so why don't reuse it?

Answer 2

That is related a lot to data you are workign with. Right now you are just producing a lot of useless trafic. I would recommend to send also some marker of current state when you are requesting are_friends.php. PHP will check if something changed using that marker and return "no changes" or updated HTML. Here you should lower server load during if nothing is changed and less trafic(suppose most request will return "no changes"). But again. It depends on what you are doing in are_friends.php, what data do you need etc.