flatArray.js

/**
 * @description Flats an array with any nested level deep. e.g. [[1,2,[3]],4] -> [1,2,3,4]
 */
export const flatArray = (arr) => {
  return (arr || []).reduce((previous, current) =>
    // call it recursivelly, adds support to nested arrays any level deep
    previous.concat(Array.isArray(current) ? flatArray(current) : current)
  , []);
}