SOURCE

let arr = [];
    let newarr = [];
    var sum_dan = 0;
    var sum_shuang = 0;
    var node = null;

    arr.push(root);
    while(arr.length !== 0 || newarr.length !== 0) {
        while(arr.length !== 0) {
            node = arr.shift();
            sum_dan += node.val;
             if (node.right !== null) {
                  newarr.unshift(node.right);
             }
             if (node.left !== null) {
                  newarr.unshift(node.left);
             }
        }
    
        while(newarr.length !== 0) {
            node = newarr.shift();
            sum_shuang += node.val;
             if (node.right !== null) {
                  arr.unshift(node.right);
             }
             if (node.left !== null) {
                  arr.unshift(node.left);
             }
        }
    }
    return Math.max(sum_dan, sum_shuang);