const queue = [];

var fn2 = (root) => {
queue.push(…root);
const {head, level} = queue.shift();
// 为了保证递归传入的数组内各个元素有效，通过 …[ ] 形式兼容
const left = head.left ? [{head: head.left, level: level+1}] : [];
const right = head.right ? [{head: head.right, level: level+1}] : [];
// 当根节点的左右数组都是空，证明是叶子节点
if(left.length === 0 && right.length === 0){
console.log(head.val, level)
return false
}
// 递归调用
fn2([…left, …right]);
}

fn2([{head: binary, level: 1}])