I'm not really a frontend dev any more but I was for a long time. I can assure you that the only reason you think your code works is because no one tells you it

I'm not really a frontend dev any more but I was for a long time. I can assure you that the only reason you think your code works is because no one tells you it's broken. If you use an error logging or telemetry service (Sentry, Rollbar, New Relic, etc) you will be aware that errors happen in frontend code all the time. It's just that most of the time bugs don't crash the app, and the user doesn't know what to expect so they see a broken feature and think it's meant to be like that.