JavaScript如何实现双向链表操作

class DNode {
 constructor(val) {
  this.val = val;
  this.prev = null;
  this.next = null;
 }
}

function add(el) {
  var currNode = this.head;
  while (currNode.next != null) {
    currNode = currNode.next;
  }
  var newNode = new DNode(el);
  newNode.next = currNode.next;
  currNode.next = newNode;
}

function find(el) {
  var currNode = this.head;
  while (currNode && currNode.el != el) {
    currNode = currNode.next;
  }
  return currNode;
}

function (newEl, oldEl) {
  var newNode = new DNode(newEl);
  var currNode = this.find(oldEl);
  if (currNode) {
    newNode.next = currNode.next;
    newNode.prev = currNode;
    currNode.next = newNode;
  } else {
    throw new Error('未找到指定要插入节点位置对应的值！')
  }
}

// 顺序
function () {
  var currNode = this.head.next;
  while (currNode) {
    console.log(currNode.el);
    currNode = currNode.next;
  }
}

// 逆序
function () {
  var currNode = this.head;
  currNode = this.findLast();
  while (currNode.prev != null) {
    console(currNode.el);
    currNode = currNode.prev;
  }
}

function (el) {
  var currNode = this.find(el);
  if (currNode && currNode.next != null) {
    currNode.prev.next = currNode.next;
    currNode.next.prev = currNode.prev;
    currNode.next = null;
    currNode.previous = null;
  } else {
    throw new Error('找不到要删除对应的节点');
  }
}