How to clean form after submitting ajax?

First of all: I tried to search the answer in the web and I found like 20 examples of code. But I failed. still nothing is working.

I'm making a simple chat and i need to clean my form after submitting data via ajax. Here is the code:

<form id="ChatFrom" class="chatMessageField" action="Amess.php" method="post">
    <input class="chatMessageField" type="text" name="mess" /><br />
    <input class="chatMessageBtn" type="button" value="Отправить" onclick="SendForm();" />
</form>

<script type="text/javascript" src="http://scriptjava.net/source/scriptjava/scriptjava.js"></script>
<script type="text/javascript">
    function SendForm() {
        $$f({
            formid:'ChatFrom',
            url:'Amess.php',
        });
    }
</script>