The only thing that bugs me about that question is that "the output of the following function" is confusingly worded. It's the sort of question that a competent candidate might get nervous about and start to overthink: wait, that isn't a function, it's a code snippet. The function here is foo – so maybe they mean "what's the output of foo"? But then what does "the output of a function" mean? I suppose they mean return value? Is this a trick question to see if I remember what push returns? Damn it, does it return the entire array or just the pushed element?
That's what my mind usually does with questions like that and I'm far from the only one. Since the goal of the test is to screen for basic competence, it ought not to filter out people who could answer the question perfectly fine if it were being asked clearly, but who also perceive corner cases and ambiguities. Such a skill should make you more likely to pass such a test, not less. Therefore the question ought to say something like "What does the following code snippet write to the console?"
