Renew <?php echo microtime();?> actual server time in pure JS

PHP
1

http://lanother.tk/msec.php :

<script src="http://code.jquery.com/jquery-1.11.0.min.js"></script>
<script>
function update(){
    $('body').load('/eho.php');
}
update();
setInterval(function(){ update() }, 1);
</script>

http://lanother.tk/eho.php :

<?php echo microtime();?>

Need pure JavaScript time from server. The simplest possible thing, please.

Thanks.