Flatten array

Flatten Array - numbers.js

const isArray = (obj) => {
  return (typeof obj === 'object' && obj.hasOwnProperty('length'));
}

function NotAnArrayException(message) {
  this.message = message;
  this.name = 'NotAnArrayException';
}

const flattenArray = list => {
  if (!isArray(list))
    throw new NotAnArrayException('The argument is not an Array!');

  const flatten = [];
  const recurse = obj => {
    if (!isArray(obj)) return;
    
    for (const item of obj) {
      if (typeof item === 'number') flatten.push(item);
      else recurse(item);
    }
  };
  recurse(list);
  return flatten;
};

console.log(flattenArray([[[1]], 2, [[3], {}, true], [10], 22])); // [1, 2, 3, 10, 22]