I think (s)he is saying to hash client side, salt, then hash again server side. So if the database gets compromised, the attacker still has to apply the salt to brute force the hash.

I can't see a reason why this hurts, but it's probably not worth it. The only benefit I can see it having is if the user reuses their passwords on other sites, as now a potential malicious MITM would have to brute force the client side hashed password in order to reuse it on other sites. They would still be able to use that client side hashed PW to authenticate to the service in question, though.

All the other websites where the users registered using the same email will only hash ONCE though!

Yeah, thats exactly my point. So the MITM who got the PW after client side hash, but before server side salt and hash would have to brute force that hash in order to use it on those other sites. That's the only benefit I see, and a very specific set of circumstances.

Is it incredibly specific? I feel like that happens time and time again when companies accidently "mitm" themselves with logs or whatever.

The first sentence is true (and I can't believe how far down this thread it first appeared), but nobody was advocating abolishing server side hashing as well.

Basically, hashing on the client does absolutely nothing for the security of the transfer or storage of the password. Whatever the client passes to the server, whether it's hashed or not, is effectively their password, and intercepting that (again, whether hashed or not) would give an attacker the actual credentials of the user.

No. The database only contains the double hash. It still needs to be bruteforced.

There is zero downside to doing an extra hash, except the chance that someone codes such a basic thing wrong.

No. Other websites on the internet, where the user also registered with the same email and password, contain the single hash.

Oh, I see. Other websites give you the 'password' to this website.

But only if neither site uses salt, so salt all your hashes. (Not even a salt is necessary here, just a site-wide addition would be fine. Or honestly you could just use a hash that wouldn't be used by a site too dumb to salt their database.)