While CodeWars is fun, my favorite part is completing a solution and comparing your answer to the many other answers people have submitted. It's such a great way to learn and you remember where you've come from. You might tell yourself, "I remember when I would've written code like that" or "That's interesting. I never thought about it that way."
This is completely different from StackOverflow. StackOverflow encourages one accepted answer. How often do you Google for a solution and simply look at the accepted answer? After you work the problem out yourself, CodeWars makes it really simple to scroll through other solutions by real people.
Here's what I mean. I pulled a few examples for you. I've also given my reaction to each solution.
Complete the keysAndValues function so that it takes in an object and returns the keys and values as separate arrays.
Simple sort, but this time sort regardless of upper / lower case.
That's why I love CodeWars. I'm not sure if signup is open to everyone, but if you need an invite, let me know.