random tip, I tend to read these like a sentence.. so 0 <= x <= 4 would read as: 0 is "less than or equal to" x and x is "less than or equal to" 4.

Wouldn't that render this kata trivial and not deserving a 5kyu rating?

the values for the x should be between those parameters

I already told you exactly which sample test your code is failing, use Pythontutor or other IDE to debug your code step by step and see what's wrong with it. Don't chain methods until you properly understand what they return in each of them, pull them apart and log what they return, you'll find out what's wrong with your code easier that way.

The tests have no problem with either method, it's your code that's trying to use them wrong, read the error message:

TypeError: Cannot read properties of undefined (reading 'toUpperCase')

undefined doesn't have toUpperCase method, that's a string method. Debug your code, add some console.log()s to help you with that. Read this: https://docs.codewars.com/training/troubleshooting

Currently, your code fails this sample test:

assert.strictEqual(generateHashtag("code" + " ".repeat(140) + "wars"), "#CodeWars")

You have to use the filter-method

Did you read the description? "have to" means it is required.

The title also says Filter in it and there is a link to MDN docs.

Your team's score will always be between 0 and 4, both inclusive.

If you know someone who would want to update 2000 JavaScript kata, let me know. If you want to update at least some of them, reach out to me at #fixing channel of Codewars Discord, and I will explain you how to do this.

Thanks!

You're missing g, h, and i there. So, the right alphabet's position is 10, not 7 as you said.