Write a Program to Find N-ary Tree Preorder Traversal

# 589. N-ary Tree Preorder Traversal

Given the root of an n-ary tree, return the preorder traversal of its nodes’ values.

Nary-Tree input serialization is represented in their level order traversal. Each group of children is separated by the null value (See examples)

### Example 1:
```
Input: root = [1,null,3,2,4,null,5,6]
Output: [1,3,5,6,2,4]
```

### Example 2:
```
Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
Output: [1,2,3,6,7,11,14,4,8,12,5,9,13,10]
 ```

Constraints:
```
The number of nodes in the tree is in the range [0, 104].
0 <= Node.val <= 104
The height of the n-ary tree is less than or equal to 1000.
```

/**
 * // Definition for a Node.
 * function Node(val, children) {
 *    this.val = val;
 *    this.children = children;
 * };
 */

/**
 * @param {Node|null} root
 * @return {number[]}
 */
 var preorder = function(root) {
    const out = [];
    const traverse = (node) => {
        if (!node) {
            return;
        }

        out.push(node.val);
        for (let i = 0; i < node.children.length; i++) {  
            traverse(node.children[i]);
        }        
        
    }
    traverse(root);
    return out;
};