Implementing Singly Linked-List using JavaScript

linkedList.js

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

class LinkedList {
  constructor(head) {
    this.head = head || null;
  }

  prepend(value) {
    let tmp = null;
    if (this.head !== null) tmp = this.head;
    this.head = new Node(value);
    this.head.next = tmp;
  }

  append(value) {
    let tmp = this.head;
    while (tmp.next !== null) tmp = tmp.next;
    tmp.next = new Node(value);
  }

  size() {
    let count = 0;
    let tmp = this.head;

    while (tmp !== null) {
      tmp = tmp.next;
      count++;
    }

    return count;
  }

  getHead() {
    return this.head;
  }

  getTail() {
    let tmp = this.head;
    while (tmp.next !== null) tmp = tmp.next;
    return tmp;
  }

  at(index) {
    let tmp = this.head;
    for (let i = 0; i < index; i++) {
      tmp = tmp.next;
      if (tmp === null) return "There is no item for this Index";
    }

    return tmp;
  }

  pop() {
    let cur = this.head;
    let prev = null;

    while (cur.next !== null) {
      prev = cur;
      cur = cur.next;
    }

    prev.next = null;
  }

  contains(value) {
    let tmp = this.head;
    while (tmp.next !== null) {
      if (tmp.value === value) return true;
      tmp = tmp.next;
    }

    return false;
  }

  find(value) {
    let tmp = this.head;

    for (let i = 0; i < this.size(); i++) {
      if (tmp.value === value) return i;
      tmp = tmp.next;
    }

    return null;
  }

  toString() {
    let tmp = this.head;
    let string = "";

    while (tmp !== null) {
      string += `( ${tmp.value} ) -> `;
      tmp = tmp.next;
    }

    return (string += "null");
  }

  insertAt(value, index) {
    if (this.head === null || index === 0) return this.prepend(value);

    let cur = this.head;
    let prev = null;

    for (let i = 0; i < index; i++) {
      prev = cur;
      cur = cur.next;
      if (cur === null) break;
    }

    const newNode = new Node(value);
    prev.next = newNode;
    newNode.next = cur;
  }

  remove(index) {
    if (this.head === null) return "List is Empty!";
    if (index === 0) return (this.head = this.head.next);

    let cur = this.head;
    let prev = null;

    for (let i = 0; i < index; i++) {
      prev = cur;
      cur = cur.next;
    }

    prev.next = cur.next;
  }
}


/*
    TESTING
*/

const head = new Node(1)            // Head Node
const list = new LinkedList(head)   // Creating a Linked List

list.append(8)      // Adds 8 at the end of Linked List
list.prepend(7)     // Adds 8 at the starting of Linked List

list.size()         // 3
list.getHead()      // Node { value: 7, next: Node {...}}
list.getTail()      // Node { value: 8, next: null }
list.at(1)          // Node { value: 1, next: Node { value: 8, next: null } }

list.pop()          // 8 is popped out from List
list.pop()          // 1 is also popped out now.

list.contains(7)    // true
list.contains(8)    // false, because we popped it earlier.

list.append(4)      // Adding some more nodes..
list.append(7)

list.find(4)        // 4's Index is 1
list.insertAt(1, 2) // 1 has been inserted between 1 & 3
list.insertAt(7, 0) // 7 has been inserted at beginning of List 

list.remove(1)      // 7 has been removed from Index 1

list.toString()     // ( 7 ) -> ( 4 ) -> ( 1 ) -> ( 7 ) -> null

Features

• append(value) adds a new node containing value to the end of the list or to start if list is empty
• prepend(value) adds a new node containing value to the start of the list
• size() returns the total number of nodes in the list
• getHead() returns the first node in the list
• getTail() returns the last node in the list
• at(index) returns the node at the given index or error message if there is no node in the requested index
• pop() removes the last element from the list
• contains(value) returns true if the passed in value is in the list and otherwise returns false
• find(value) returns the index of the node containing value, or null if not found
• insertAt(value, index) inserts a new node with the provided value at the given index or at the end of the list if index is bigger than list size
• removeAt(index) removes the node at the given index or error message if the list is empty or if the request index is bigger than list size
• toString() returns your LinkedList objects as strings in the format: ( value ) -> ( value ) -> ( value ) -> null