> or have it done as part of the standard functions like `map`.

Which are all well and good when they are applicable, which is not always 100% of the time.

> Because I usually do checks against the length of the array

And what do you have your code do if such "checks" fail? Throw an assertion error? Which is my whole point, I'm advocating in favor of sanity-check exceptions.

Or does calling them "checks" instead of "assumptions" magically make them less brittle from surrounding code changes?