Once you have 3 environments (which IMHO is the minimum viable number: dev, staging, prod), it tends to be much easier to generalise that to N, at least from the application side (spinning up the extra infra is a separate beast). It tends to weed out many of the "if (prod)"s because there should now be differences between dev & staging that you need to take care of, and sprinkling elaborate switch statements gets tedious really fast - most devs tend to be happier actually simplifying code.

I've seen some really nasty offenders though, e.g. actual business logic hidden behind an "if (window.location.hostname == ...)". Sometimes it takes a lot of patience to explain that this is how you get production-only bugs that QA will never have a chance to find or reproduce.