redirect to alredy open tab on same button click if open

Question

hi,

 

on a button click i am redirecting to a page in new tab by below code:

 

 <asp:Button ID="Button1" Text="CHAT" runat="server" CssClass="btn btn-primary" OnClick="Button1_Click" OnClientClick="document.forms[0].target ='_blank';"/>

 

but if i again click on that button again then the page must redirect to already opened tab it should not open the new tab again 

 

Thanks.....