I read that as filter out any odd squared number

Needs a fixed test with fSquared([0]). My solution would bug out on that.

Having different output types is bad.

Node 12 should be enabled.

Added.

Wording was different when I raised the issue

It's already there

There is a square each item before filter the odd numbers ;-)

I might specify in the description that we should return undefined in case some element in the array is not a number.

Needs random tests.

No random tests yet ..

The description seems wrong.

It says return the sum of the even numbers

In fact it is expecting the sum of the squares of them

This is fine. :]

So the directions were not very well written. Rewrote them. Hopefully they are more clear. Feel free to look again and see if there is further input you'd like to give.

As always, thanks for the feedback.

Sure, let me give it a look.