How to call server side function on client side

Hi,
   How to call server side function on client side? here i want to call change() function on textbox onchange event.

  <script language="javascript">
    function serverfunction()
    {
    }
    </script>
<input id="Text1" onchange="javascript:serverfunction();"  type="text" />

code behind:
  public void change()
    {
        Response.Write("hello");
    }
...