Overly defensive programming

I’ve kind of been following the development of optional chaining in JavaScript. It’s now stage 3, which had me re-evaluating my own thoughts on the syntax. @housecor has been a visible opponent of the syntax and I found this piece via a thread on his twitter. It has some good points specifically relevant to optional chaining, but even more broadly relevant to writing JS applications.

Trust in your data, and your code will be more predictable and your failure cases more obvious. Data errors are simpler to debug if an error is thrown close to the source of the bad data.

Unnecessary safety means that functions will continue to silently pass bad data until it gets to a function that isn’t overly safe. This causes errors to manifest in a strange behavior somewhere in the middle of your application, which can be hard to track...Debugging it means tracking the error back to find where the bad data was introduced.

And later:

Being overly cautious with external data means that the next person to consume it doesn’t know if it’s trustworthy, either. Without digging into the source to see how trustworthy the data is, the safest choice is to treat it as unsafe. Thus the behavior of this code forces other developers to treat it as an unknown, infecting all new code that’s written.