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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.
Scroll down the comments to one that was made about 6 years ago. I've replied with a detailed explanation that should help you understand.
If you're new to Javascript, I highly recommend checking out this great free and up-to-date tutorial - https://javascript.info.
And for reference purposes, you can use this resource - https://developer.mozilla.org/en-US.
Sorry for such a late reply. This is the spread syntax. You've probably already searched for it, but if not, you can find out more about it here - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax.
Use regex101.com for analyzing regular expressions.
what ... in beginning of array stands for?
I did string.match(/[a-z]/g) but it return just amount of letter this string contains(not amount of unique letters), why it wasnt working? Can anyone explain please