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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.
think of ...vals as of the 'rest' arg which is a collection of everything what you call the function with after the positional arguments. In this concrete example calling scoreTest with (str, right, omit, wrong) will map to str -> str and vals -> [right, omit, wrong]. V arg of the reduce's callback is a value from your str collection (an answer to the question in the test), so vals[v] will return you the number of points for right, omit or wrong answer and [1,1,-1] array simply gives you a sign you should use with this value. '() => expressions' is a way to define lambda in ES6