Passing the javascript variable value to code behind Using C#

In previous post we have seen how to pass variable from server side to client side,get filename from path in javascript,Is there any method to pass JavaScript value to server side?This query raised when i work with java variable in asp.net.Here i will also give an simple tip for new one's which are workd on javascript in asp.net.Many of that get doubt "how to write java script" in asp.net .We can write java script in asp.net as write in html page. "Using hidden field we can pass v javascript  variable from client side to server side".For this i just write a simple javascript function to assign the java variable to asp hidden control.Then we can access the hidden field value and assign to text box .

Function test()
{
  int i=10;
  var hiddentest = '';
document.getElementById('<%= hiddentest.ClientID%>').value = i;
 }

Default.aspx

<asp:HiddelFiled runat="server" id="test"></asp:Hiddenfield>
<asp:textbox runat="server" id="eletext"></asp:textbox>

The id of the hidden field is used to assign the JavaScript variable value

Code behind Page(.cs):

protected void Page_Load(object sender, EventArgs e)
{
eletext.text=test.value; 
}