Not able to access hidden control value in javascript

See more:

C#

ASP.NET

Javascript

C#4.0

In Code Behind

protected void Button1_Click(object sender, EventArgs e)
   {
   set();
   }
public void set()
   {
       string s = "10";
       HiddenField1.Value = s;
   }

In Aspx Source

<script language="javascript" type="text/javascript">

function get() {
           var s = form1.HiddenField1.value;
           alert(s);
       }

</script>

<asp:Button ID="Button1" runat="server" onclick="Button1_Click" OnClientClick="get()" Text="Button" />

i have a hidden field and iam setting its value in set method in the above code
now i just want to access that value into my javascript's Function named Get

but iam faceing little diffretn output than expected

: the output is like this

1. when i click the button for the first time i get an empty alert but wen i click again am getting the the value i gave

2. When i hardcode the value in the page_load its taking only that value n not getting updated during remaining code execution