import { flatten } from "array-flatten";

flatten([1, [2, [3, [4, [5], 6], 7], 8], 9]);
//=> [1, 2, 3, 4, 5, 6, 7, 8, 9]

(function() {
  flatten(arguments); //=> [1, 2, 3]
})(1, [2, 3]);