Some JavaScript interview questions

[Cay Horstmann]

I dislike interview questions that probe things that programmers should not normally be doing--like asking what the value of [3] * true is. But here are a few questions that I think are pretty good.

1. What is a after the following?
let a = [1, 2, 3, 4] for (i in a) { if (i > 0) a[i - 1] = a[i] }

This just tests understanding of the in operator.

2. What is a after the following?
let a = [1, 2, 3, 4] for (i in a) { a[i - 1] = a[i] }

That's more interesting. What happens with a[-1]?

3. How about
let a = [1, 2, 3, 4] for (i in a) { if (i !== 0) a[i - 1] = a[i] }

This brings up an interesting fact about array indexes...which should allow the candidate to ace the following:

4. What is a after the following?
let a = [1, 2, 3, 4] for (i in a) { if (i < a.length - 1) a[i] = a[i + 1] }

Which brings up the depressing reality how hard it is to avoid cruft from the ages.