更新评论主题的内容而不会打扰“添加评论”

how do i refresh the contents of a div 'comment thread' without disturbing users input on the text field.Like in Facebook comment section ? I am using Php, Jquery, Javascript.

var auto_refresh = setInterval(
    function autorefresh()
    {
        var ipo = document.getElementById('commentarea');
        $('#commentarea').load('processing.php');
    }, 
    100);

The processing.php includes a while loop where all the div i.e. main content,like,comment is present.What i want to do is when user clicks on comment a div comes under it where other's comment are displayed and text field is displayed for users comment,similar to Facebook's comment view. How do I refresh the contents of the comments without disturbing the user's comment field.