How to change an asp c# public variable from js?

I'm working at Microsoft visual web developer 2010 express with aspx project. And I'm trying to change a public variable from the c# code in the js code. But I couldn't find how. can anyone help me? thx.

So I have this var in my c# code

public partial class ASPX_Page : System.Web.UI.Page
{
 public bool check = false;
}

And I want to change it in my js function.

function myfun() {
//here I want to change check to true
}

I thought about creating an invisible asp obj and change its value. But I think it's not the right solution... Is there an other accepted solution?