doublylinkedlist.js

// 2 <-> 8 <-> 10 <-> 4 <-> 3 <-> 6 <-> 7

// {prev, value, next}

class Node {
  constructor(value) {    
    this.prev = null;    
    this.value = value;
    this.next = null;
  }
}

class DoublyLinkedList {
  constructor(mainNode) {
      this.headNode = mainNode;
  }
  
  add(node) {
    let pointer = this.headNode;

    while(pointer.next) {
      pointer = pointer.next;
    }
    
    pointer.next = node;
    node.prev = pointer;
  }
  
  insert(value, beforeValue) {
    let pointer = this.headNode;
    
    const node = new Node(value);

    while(pointer.next) {      
      pointer = pointer.next;      

      if(pointer.value === beforeValue) {
        node.next = pointer.next;        
        
        if(pointer.next) {
          pointer.next.prev = node;
        }
        
        pointer.next = node;
        node.prev = pointer;
      }
    }                   
  }
  
  remove(value) {
    let pointer = this.headNode;

    while(pointer.next) {
      if(pointer.next.value === value) {
        pointer.next = pointer.next.next;

        if(pointer.next) {
          pointer.next.prev = pointer;
        }
        
      } else {
        pointer = pointer.next;
      }
    }               
  }
  
  printAll() {
    let pointer = this.headNode;
    
    let str = this.headNode.value;

    while(pointer.next) {
      pointer = pointer.next;
      str += ' <-> ' + pointer.value; 
    }                      
    
    console.log(str);
  }
}


const headNode = new Node('HEAD'); // {null, 'HEAD', null}

const dll = new DoublyLinkedList(headNode);

dll.add(new Node(2));
dll.add(new Node(8));
dll.add(new Node(10));
dll.add(new Node(4));
dll.add(new Node(3));
dll.add(new Node(6));
dll.add(new Node(7));

dll.printAll();

dll.remove(7);
dll.add(new Node(33));
dll.remove(10);
dll.printAll();

dll.insert(100, 4);
dll.insert(55, 33);
dll.printAll();

dll.add(new Node(1));

dll.printAll();