A JS function to recursively flatten an array

flattenArray

/**
 * deeply flattens the content of an array recursively
 * @param {Array} arr - the array to flatten
 * @param {Array} acc - the accumulator array object
 */
function DeepFlatten(arr, acc) {
  if (!(arr instanceof Array)) return acc.push(arr);
  arr.forEach((value) => DeepFlatten(value, acc));
  return acc;
}

/**
 * flattens the content of an array
 * @param {Array} arr - the array to flatten
 */
function flatten(arr) {
  return DeepFlatten(arr, []);
}

var a = [
  1,
  2,
  [3, 4, 5],
  6,
  7,
  [8, 9, 10],
  [11],
  12,
  13,
  14,
  [15, 16, 17, [18, 19, [20, 21, [22, 23, 24], 25, [26, [27, 28]], 29, 30]]],
];

console.log(flatten(a));