comment_submit.php

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.0/jquery.min.js">

<script type="text/javascript" >
$(function() {
$(".comment_button").click(function() {

var test = $("#content").val();
var dataString = 'content='+ test;

if(test=='')
{
alert("Please Enter Some Text");
}
else
{
$("#flash").show();
$("#flash").fadeIn(400).html('<img src="ajax-loader.gif" align="absmiddle"> <span class="loading">Loading Comment...</span>');

$.ajax({
type: "POST",
url: "demo_insert.php",
data: dataString,
cache: false,
success: function(html){
$("#display").after(html);
document.getElementById('content').value='';
document.getElementById('content').focus();
$("#flash").hide();
}
});
} return false;
});
});
</script>
// HTML code
<div>
<form method="post" name="form" action="">
<h3>What are you doing?</h3>
<textarea cols="30" rows="2" name="content" id="content" maxlength="145" >
</textarea><br />
<input type="submit" value="Update" name="submit" class="comment_button"/>
</form>
</div>
<div id="flash"></div>
<div id="display"></div