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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
Yeah, a function taking two arrays as arguments would have been more appropriate.
In Javascript extending native prototypes is bad practice. So in that regard this kata is not worthy of 4th kyu.