flatten an array of arbitrarily nested arrays of integers into a flat array of integers

flat_numeric_arr.js

'use strict'

/**
 * flatten an array of arbitrarily nested arrays of integers into a flat array of integers
 */
function flat_numeric_arr(x, res) {
  res = res || [];
  if (typeof x === 'number') {
    res.push(x);
  } else if (Array.isArray(x)) {
    x.forEach((y) => {
      flat_numeric_arr(y, res);
    })
  } else {
    // throw 'improper argument type'; // ok, just ignore for now
  }
  return res;
}

// let a = [1,2,[3, 4], 'w', 5,[[6,7,8], 9, 10]];
// let b = flat_numeric_arr(a);
// console.log(b); // [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]