Hidden field value for different user

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ASP.NET

I have created one page having textbox,button and many more controls.
User can write text in textbox,I am calling javascript function on keyup of textbox.Javascript function count letter entered into textbox.If it is greater than 80,it check the checkbox.User is able to see checked checkbox.

Every thing is working fine.On button click event I am getting checkbox.checked = false if user has already seen checkbox is checked.So I have created javascript function which I call on button click event,in that function I am checking, checkbox is checked or not. if it is checked assigning 1 to hidden field if not zero.I know hidden field is client side management and it is at page level.

Now my question is if there 3 user,everybody is writing at same time,everybody will get value he/she set or diff?

What I have tried:

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

function CheckStatus()
{

if (document.getElementById('ChkMsg').checked == true)
{
document.getElementById('hiddenfieldIschk').value = '1';
}
else
{
document.getElementById('hiddenfieldIschk').value = '0';
}
}
</script>

<asp:Button ID="btn" runat="server" Onclientclilck="return CheckStatus();" onclick="btn_Click1" />
<input type="hidden" id ="hiddenfieldIschk"  runat="server" />