Yes, but if you press 'back' you get a split-second view of the previous page before being redirected to the error page again. In general, don't use unconditio

Yes, but if you press 'back' you get a split-second view of the previous page before being redirected to the error page again. In general, don't use unconditional in-page redirects, whether they be javascript or meta refresh. If you want to do a redirect like that, you can have your server serve a 301 and the browser will collapse history appropriately, but if you must do it in JS then use history.replaceState.