Read this: https://www.codewars.com/kata/5a34af40e1ce0eb1f5000036/discuss#6478df8fe58a25005c6ddb2d

You have the same problem. The third post below yours.

Your code is wrong, once again. And tested with the same input (for God's sake, learn that for once) it will fail in VSCode too. Your code doesn't have a problem with toLowerCase at all, read the error message:

Testing ",vx:+xi?"
expected ' 22 24   24 9 ' to equal '22 24 24 9'

And this part of the description again:

If anything in the text isn't a letter, ignore it and don't return it.

Your code adds some spaces when it shouldn't.

The mistake is once again in your code, see which input makes your code fail and debug your code, please.

Read the description again, your code isn't 100% right, and please stop posting "as always it works in vscode and not here" if you don't use the exact same input in both places, that's what would happen.

The kata is fine; I am the 12,880th person to succesfully solve it in JavaScript.

This means you rather instead should not like the incomplete coverage of tests in your VSCode environment.

Just print the input: https://docs.codewars.com/training/troubleshooting#print-input

For once, it was the tests that were faulty, try again.

"Under" unambiguously means "less than".

Description says: Define String.prototype.toAlternatingCase [...]. Your solution is wrong.

Everything is in the title: Filter out the geese.

Remove static keyword, the initial code hadn't it. Read about when and how to use it: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/static

Don't rename the class, the tests won't find it. Codewars is not the problem here, you're using your code in VSCode in a different way, that's why it works there and not here.

Try your code in VSCode calling it like this:

let sif = new SIF()
sif.findSmallestInt(arr1)

And see how it won't work there either.

Look where the closing quote is in the error message, the input is not '123' there. Not a bug. The post below yours is about the same, please read it.

Take a closer look at initial solution template you get when you enter the trainer.

No it doesn't, surely you're calling the method with an argument, like this:

toJadenCase("How can mirrors be real if our eyes aren't real")

And here it's called like this:

var str = "How can mirrors be real if our eyes aren't real";
Test.assertEquals(str.toJadenCase(), "How Can Mirrors Be Real If Our Eyes Aren't Real");
                        ^
                       see? 

It's not a problem with CW, what does your code return without the 0 in VSCode and codepen when the input is []? You just didn't test your code there with that input there.