Algorithm: Symmetric Tree

/**
 * Definition for a binary tree node.
**/

class TreeNode
{
    constructor(val, left, right)
    {
        this.val = val
        this.left = left
        this.right = right
    }
}

/**
 * @param {TreeNode} root
 * @return {boolean}
**/
let isSymetric = (root) =>
{
    let listOfNodes = [ root ]

    return isListSymetric(listOfNodes)
}

let isListSymetric = (listOfNodes, symetric = true) =>
{
    let listLength = listOfNodes.length

    for(let i = 0; i < listLength; i++)
    {
        let currentNode = listOfNodes[0]

        if (currentNode.left !== undefined)
            listOfNodes.push(currentNode.left)

        if (currentNode.right !== undefined)
            listOfNodes.push(currentNode.right)

        listOfNodes.shift()
    }
    
    if (listOfNodes.length % 2 !== 0)
        return false

    for (let j = 0; j < listOfNodes.length / 2; j++)
        if (listOfNodes[j].val !== listOfNodes[listOfNodes.length - 1 - j].val)
            return false;

    if (listOfNodes.length > 0 && symetric == true)
        symetric = isListSymetric(listOfNodes, symetric)

    return symetric;
}

// left side
let tree4 = new TreeNode(3)
let tree5 = new TreeNode(4)
let tree2 = new TreeNode(2, tree4, tree5)

// right side
let tree6 = new TreeNode(3)
let tree7 = new TreeNode(4)
let tree3 = new TreeNode(2, tree7, tree6)
let tree1 = new TreeNode(1, tree2, tree3)