Deeply Flatt Array

flattenArray.js

// @flow

const flattenDeep = (arr: Array<number>], flatArr = []) => {
  const length = !arr ? 0 : arr.length;
  let index = 0;
  while(index < length) {
    if (Array.isArray(arr[index])) {
			 flatDeep(arr[index], flatArr);
		} else {
			flattArr[flattenArr.length] = arr[index];
		}
		index += 1;
  }
	return flatArr;
}

const flattenArray = (arr: Array<number>) => {
	return flattenDeep(arr);
};

export default flattenArray;