const arr = [1, [2, [3, 4, [5, [6, 7, 8]]]]]; const flatArr = (arr) => arr.reduce( (acc, curr) => Array.isArray(curr) ? [...acc, ...flatArr(curr)] : [...acc, curr], [] );
const arr = [1, [2, [3, 4, [5, [6, 7, 8]]]]]; const flatArr = (arr) => arr.reduce( (acc, curr) => Array.isArray(curr) ? [...acc, ...flatArr(curr)] : [...acc, curr], [] );