Flatten array iterative and recursive

const flattenArrayIterative = (arr) => {

const stack = [arr];

const result = [];

while(stack.length) {

const list = stack.pop();

for (const val of list) {

if (Array.isArray(val)) {

stack.push(val);

} else {

result.push(val);

}

}

}

return result;

};

const flattenArrayRecursive = (arr) => arr.reduce((acc, curr) => acc.concat(Array.isArray(curr) ? flattenArrayRecursive(curr) : curr), []);

const nums2 = [2, 4, [5, [[4, [21, [56, [28]]], 90]]], 9, 2, 4, [5, [[4, [21, [56, [28]]], 90]]], 9];

console.log(flattenArrayIterative(nums2).sort());

console.log(flattenArrayRecursive(nums2).sort());