HOW TO HIDE AND SHOW DIV AT JAVASCRIPT

function ShowDiv()
{

document.getElementById('<%=div_reply_to_thread.ClientID %>').style.display='block';
document.getElementById('<%=td_btn_reply.ClientID %>').style.display='block';
document.getElementById('<%=td_btn_edit.ClientID %>').style.display='none';
}
function HideDiv()
{
document.getElementById('<%=div_reply_to_thread.ClientID %>').style.display='none';
}