text: /**
   * // Definition for a Node.
   * function Node(val,children) {
   *    this.val = val;
   *    this.children = children;
   * };
   */
  /**
   * @param {Node} root
   * @return {number[]}
   */
  var postorder = function(root) {
      var result = []
      function helper(node){
          if(node){
              for(let i = 0; i<node.children.length;i++){
                  helper(node.children[i]);
              }
              result.push(node.val)
          }
      }
      helper(root)
      return result
  };