JavaScript redirects are one of the methods available to webmasters in communicating to both users and search engines that the requested URL is unavailable, either permanently or temporarily. The URL you are then served should be seen as the alternative or new permanent.
Typically best practice echoes that you should use server-side 301s, 302s, or 307s.
Usually, servers hosting JavaScript (JS) applications are Nginx servers, with configuration files where one can always implement server-side redirects, which is the recommended way by Google.
