LinkedList.js

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

class LinkedList {

  constructor() {
    this.head = null;
    this.tail = null;
  }

  get isEmpty() {
    return this.head === null;
  }
  
  add(value) {
    const node = new Node(value);
    if (this.head === null) {
      this.head = this.tail = node;
      return this;
    }
    this.tail.next = node;
    this.tail = node;
    return this;
  }
  
  addHead(value) {
    const node = new Node(value);
    node.next = this.head;
    this.head = node;
  }

  removeHead() {
    if (this.isEmpty) {
      return null;
    }
    const head = this.head;
    this.head = this.head.next;
    return head.value;
  }
  
  removeTail() {
    if (this.isEmpty) {
      return null;
    }

    const {
      value
    } = this.tail;
    if (this.head === this.tail) {
      // List with single node.
      this.tail = this.head = null;
      return value;
    }

    let prev = null;
    let current = this.head;
    while (current.next !== null) {
      prev = current;
      current = current.next;
    }

    // Adjust tail pointer.
    prev.next = null;
    this.tail = prev;

    return value;
  }

  remove(x) {
    let prev = null;
    let current = this.head;
    while (current !== null) {
      const {
        value,
        next
      } = current;
      if (value !== x) {
        prev = current;
        current = next;
        continue;
      }
      // If value is at head.
      if (prev === null) {
        this.head = next;
      } else {
        prev.next = next;
      }
      return x;
    }
    return null;
  }
}

const list = [2, 1, 3, 4, 5].reduce((list, value) =>
  list.add(value), new LinkedList());