constlevelOrder=function(root){if(root==null)return[]constresult=[]constqueue=[root]while(queue.length>0){constlevelSize=queue.lengthconstlevel=[]for(leti=0;i<levelSize;i++){consthead=queue.shift()for(constchildofhead.children){queue.push(child)}level.push(head.val)}result.push(level)}returnresult}