JavaScript Arrary flat functions

Flatten.js

// Use recursion
function flatten(arr) {
  let result = [];
  arr.forEach(el => {
    if (el instanceof Array) {
      result = result.concat(flatten(el));
    } else {
      result.push(el);
    }
  });
  return result;
}

// Without use recursion
function flatten(arr) {
  while (arr.some(item => Array.isArray(item))) {
    arr = [].concat(...arr);
  }
  return arr;
}