So you have not passed it.

I have passed the test but said failed when attempt

Testing doesn't handle this.

The description says nothing about how duplicate x's should be handled.

I never decalre them unless they're needed.

You should, but it's not required. This way a function pollutes the global scope, and that's bad.

wow! Don't you have to declare const or let before the function expression name?

Still missing random tests.

Welcome in 2018.

Not too bad. Good job!

There's a couple of minor grammar errors in the description that need fixing to avoid confusion (and to just read better):

• case-sensitive vowel should be case-insensitive vowel
• (discluding y) should be (excluding y)
• "Keep your eyes peel Dora!" should be "Keep your eyes peeled Dora!"

You haven't actually added random tests yet, but seeing as there are 21 fixed tests I'll let you pass ;)

Added more test coverages. Thank you all kindly :)

Try https://github.com/codingforeveryone/READMEs/blob/master/codewars/random-test-cases-for-complete-beginners.md :-)

Ah thanks! This is my first kata, so I'm not quite familiar with the process - how do you add randomly generated test cases?

Your Kata needs more extensive test coverage to prevent easy cheap-cheat solutions and/or logically flawed solutions. The most common way to increase test coverage is through the inclusion of randomly generated test cases at runtime so please add these. The lack of test coverage in a Kata as an Issue is recognised as an official CW stance.