For example:
procedure TMainForm.UniButton1Click(Sender: TObject);
begin
//UniSession.AddJS('window.open(''https://www.google.com'', ''_blank'');'); // to open a new window/tab
end;
UniButton1.ClientEvents.ExtEvents ->
function click(sender, e, eOpts)
{
window.open("https://www.google.com", "_blank");
}
...