JS native immutable array methods
Reduced from https://gist.github.com/rauschma/f7b96b8b7274f2e2d8dab899803346c3
Methods
concat(...items: (T | Array<T>)[]): T[]
ES3
Returns a new array that is the concatenation of this
and all items
. Non-array parameters are treated as if they were arrays with single elements.