Try lookup how for in works.

Your solution returns a blank array, it should have returned an array with "a" and "b".

I have also got the same problem with this approach. Use setFullYear() instead of new Date().

What hint do you recommend?

Details states: "To make things simpler, it will only have to deal with simple values and objects and arrays containing strings, booleans and numbers, without taking into account regular expressiones, dates and functions"

One of the submit tests includes an array with an object.
[ 1, 2, null, undefined, { name: 'Joe' } ]

I recommend to 1) update the detail to state arrays containing objects, string, booleans, and numbers or 2) remove the test.

Many thanks for looking over my code and spotting this :)

Can someone give insights into the below test spec:

"Returns names of two arguments for a function that takes in two arguments, written in another way - Expected: ["a","b"], instead got: []"

Totally agree - the confusion is with how the Date object works whereby months start from 0 (January) and not 1 (February)

I think the instructions are misleading. You are talking about the 16th of October in 1990, which was actually a Tuesday (and not a Friday). The object new Date (1990, 10, 16) refers to Friday, the 16th of November in 1990, since months are starting at 0.

Hi Richard, you are correct.
I've changed a description. Thanks for spotting it.