Loading collection data...
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.
the object key and value,let key as the item,value as the count of the item!
How clever!
while i=0, it[-1]=undefined,js don't throw error
arr.filter is really useful! thank you!
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