An attacker knowing what hash function you used does not reduce your hash security in any material way. The most secure thing you can do is to use just regular

An attacker knowing what hash function you used does not reduce your hash security in any material way. The most secure thing you can do is to use just regular out-of-the-box Argon2 or scrypt hashing. And even if an attacker knows the exact code of the Argon2 function you used to hash, they are no closer to cracking it. In fact, customizing it in any way is almost certain to reduce your security. Hashing password client-side is a terrible idea (not only is it a terrible idea but it's pretty much useless in terms of security), but it's not because of someone being able to "get" your hash function.