function post_comment() {
    xmlHttp=GetXmlHttpObject()
    if ( xmlHttp == null ) {
        alert("Browser does not support HTTP Request");
        return;
    }
    
    if( document.getElementById('comment_error') )
        document.getElementById('comment_error').style.display = 'none';
    document.getElementById('comment_issaving').style.display = 'block';
    
    var user = '';
    
    if( document.getElementById('comment_form_user') )
        user = document.getElementById('comment_form_user').value;
    
    var url = root + 'ajax/comments.php';
    var params = 'product=' + document.getElementById('comment_form_product').value + 
                '&email=' + document.getElementById('comment_form_email').value +
                '&name=' + document.getElementById('comment_form_name').value + 
                '&comment=' + document.getElementById('comment_form_text').value + 
                '&user=' + user;
    
    xmlHttp.open("POST", url, true);
    xmlHttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    xmlHttp.setRequestHeader("Content-length", params.length);
    xmlHttp.setRequestHeader("Connection", "close");
    xmlHttp.onreadystatechange = function() {
        if( xmlHttp.readyState == 4 && xmlHttp.status == 200 ) {
            document.getElementById('comments').innerHTML = xmlHttp.responseText;
            document.getElementById('comment_issaving').style.display = 'none';
            clear_comment_form();
        }
    }
    xmlHttp.send( params );
}

function clear_comment_form() {
    document.getElementById('comment_form_name').value = '';
    document.getElementById('comment_form_email').value = '';
    document.getElementById('comment_form_text').value = '';
}