Well ok, but it still doesn't work here, because your code is flawed. Check it again with str of a few spaces.

TypeError: Cannot read property 'toUpperCase' of undefined
but the code is working perfectly in the browser console

Hi, there are lots of tests with a similar input so it's hard to tell which one you are failing on: try printing the input so you can see what the string being passed to your function actually looks like:

https://docs.codewars.com/training/troubleshooting/#error-messages-and-printing-your-inputoutput

Then you can "debug" manually, by comparing your code to the conditions given in the description. For example maybe your code is failing due to whitespace, capital letters, empty string etc.

Hi, who could helps me with '#CodeWars' error, should return false, I returning that value, but tests didn't pass(JS ). I could share link on CodePen.