Nothing specific to React but having both client-side and server-side validation means that any deficiencies of server-side validation will be concealed and go unnoticed (until exploited by an attacker).

In contrast, server-side validation only means any validation deficiencies are more likely to be discovered during legitimate usage since the client-side validation is no longer covering up for it.

I think you have it backwards. You _first_ do server-side validation, then you add client-side validation _as an optimization_, so that invalid requests are not even sent.

My point is that once you do that any subsequent deficiencies in your server-side validation become invisible during normal usage (because the client-side validation will prevent you from even trying).

Actual hackers, the ones who try to hack your e-commerce site.

For such things, if you're not doing everything Server Side to Render fully validated and sanitized data safely, you should be.

If you do server-side rendering of your React application, then it would be very similar to htmx from that perspective.

If it’s is purely a SPA, then all business logic would be behind secure APIs, so I don’t really understand your point.

That sounds like an irrational fear of front-end.

SPAs require implementing safety checks on both sides in 2 different languages. Many junior devs believe the client code is trustworthy and put important validation only in the client. I’ve worked with many codebases like this. If there’s only one place to specify validation, it should always be the server. So server side frameworks have this built in to their model and thus are less susceptible to this whole class of bugs.

> SPAs require implementing safety checks on both sides in 2 different languages.

This isn't exclusive to SPAs. For example, I am a .Net dev, and I have both front-end and back-end validation in most of my applications without ever using any SPA frameworks.

If I am in a pinch for time, I sometimes just drop front-end validation completely, and let the server handle the validation and then have the front-end handle the server validation responses accordingly.

>SPAs require implementing safety checks on both sides in 2 different languages.

Nodejs is quite popular. One language works on front-end and back-end. Like any language, security is up to the developers.

>Many junior devs believe the client code is trustworthy and put important validation only in the client.

Who is letting "junior devs" make these decisions? It sounds like they deserve to be hacked.

I’m guessing the issue is devs putting business logic constraints in the client and not duplicating them in the server