Implementation of Doubly Linked List in JavaScript
Last Updated :
28 Apr, 2025
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This article will demonstrate the Implementation of Doubly Linked List In JavaScript.
A doubly linked list (DLL) is a special type of linked list in which each node contains a pointer to the previous node as well as the next node of the linked list.
Doubly Linked List in JavaScript
To create we have to create the following classes:
- Node Class: To implement and create elements and link other elements.
- Doubly Linked List Class: To store and access all nodes of the list.
Doubly LinkedList Node is constructed of the following items
- A class named node
- A class constructor, and
- Data items/variables
- data: to contain respective node value
- next: to link the next node with the default value as null.
- prev: to link the previous node with the default value as null.
Example:
// Doubly Linked list Node
class Node {
// Constructor to create a new node
// next and prev is by default initialized as null
constructor(val) {
// To store the value
this.data = val;
// To link the next Node
this.next = null;
// TO link the previous Node
this.prev = null;
}
}
Doubly Linked List is constructed of the following items
- Class Named DoublyLinkedList
- A constructor to create the DLL
- Data items/variables:
- head: to store the starting node
- tail: to store the ending node
Example:
// Doubly Linked List
class DoublyLinkedList {
// Constructor to create a new linked list
constructor() {
// To contain the first item of the list
this.head = null;
// To contain the last item of the list
this.tail = null;
}
}
Basic Operations in Doubly Linked Lists:
Method to Check if the List is Empty:
- Check if the head is null or not and return result
// To check if the list is empty
isEmpty() {
if (this.head == null) return true;
return false;
}
Method to Insert Element:
- Create a new node with value as argument
- Check if the head is null insert at head
- Else insert the new node at the tail and shift tail pointer
// Method to add item at the last of doubly linked list
addItem(val) {
// Create a temporary variable
let temp = new Node(val);
// If the list is empty link assign
// new node to both head and tail
if (this.head == null) {
this.head = temp;
this.tail = temp;
}
// else add item to the tail and shift tail
else {
temp.prev = this.tail;
this.tail.next = temp;
this.tail = this.tail.next;
}
}
To traverse and display the list:
- Check is the list is not null
- Use a current poiter to treaverse the list and display value using console.log()
// To traverse and display the list
display() {
// Check if the List is empty
if (!this.isEmpty()) {
// traverse the list using new current pointer
let curr = this.head;
while (curr !== null) {
// Display element
console.log(curr.data);
// Shift the current pointer
curr = curr.next;
}
}
}
Implementation of Doubly Linked List
Example: This example demonstrate the basic implementation of a link list.
// Doubly Linked list Node
class Node {
// Constructor to create a new node
// next and prev is by default initialized as null
constructor(val) {
// To store the value
this.data = val;
// To link the next Node
this.next = null;
// TO link the previous Node
this.prev = null;
}
}
// Doubly Linked List
class DoublyLinkedList {
// Constructor to create a new linked list
constructor() {
// To contain the first item of the list
this.head = null;
// To contain the last item of the list
this.tail = null;
}
// To check if the list is empty
isEmpty() {
if (this.head == null) return true;
return false;
}
// Method to add item at the last of doubly linked list
addItem(val) {
// Create a temporary variable
let temp = new Node(val);
// If the list is empty link assign
// new node to both head and tail
if (this.head == null) {
this.head = temp;
this.tail = temp;
}
// else add item to the tail and shift tail
else {
this.tail.next = temp;
this.tail = this.tail.next;
}
}
// To traverse and display the list
display() {
// Check if the List is empty
if (!this.isEmpty()) {
// traverse the list using new current pointer
let curr = this.head;
while (curr !== null) {
// Display element
console.log(curr.data);
// Shift the current pointer
curr = curr.next;
}
}
}
}
// Create new Doubly Linked List
const dll = new DoublyLinkedList();
// Add elements in the list
dll.addItem(25);
dll.addItem(27);
dll.addItem(17);
dll.addItem(29);
// Display the list
dll.display();
Output
25 27 17 29
