链表取中间节点

const head = {
  'val':1,
  'next':{
      'val':2,
      'next':{
          'val':3,
          'next':{
              'val':4,
              'next':{
                  'val':5,
                  'next':undefined
              }
          }
      }
  }
}

class Node{
    constructor(element,next = null){
        this.element = element
        this.next = next
    }
}

const getElementAt = function (position,node) {
  let dummyNode = new Node(-1,node)
  let size = 0
  while(dummyNode.next){
    size ++
    dummyNode = dummyNode.next
  }


 if(position >= 0 && position <= size) {
   for (let i = 0; i < position; i++) {
     node = node.next;
   }
   return node;
 }
 return undefined
};

console.log(getElementAt(1,head))