You should check for other input types too.

If parameter is not an Integer (eg String, Array) method should return false as well.

Also, your code will fail for 16 (Power of 4) because Math.sqrt(Math.sqrt(16)) --> Math.sqrt(4) --> 2, but 2 is not divisible by 4.

As of now, Enumerable Series and Training JS Series have been created. So there's already plenty of tutorial-based katas. You can search them with tutorial tag, hence closing this suggestion!

OP solved it, closing!

'Looks like you've solved it'

not a kata suggestion

The number of random tests increased.

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Fixed

Raised as an issue.

Amazing solution.
Does this work on 4 digits numbers?

For example digital_root(1234) => 1

There are examples.

Search across "all" languages - there are 59