I separately assume a salt is part of my hash function. Salts only help with rainbow tables (an admirable goal, but not my one here).

I can trust the site to deploy the correct javascript more than I can trust it not to steal passwords because

- That is auditable - it is impossible for a malicious site to do so without risking being caught.

- The HTML/JS can be served from static cloud storage that is far less likely to be hacked than the server running a DB verifying passwords.