with head & tail

linkedlist.js

// 2 -> 8 -> 10 -> 4 -> 7

// {value, next}

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

class LinkedList {
  constructor(mainNode) {
      this.headNode = this.tailNode = mainNode;
  }
  
  add(node) {
    this.tailNode.next = node;
    this.tailNode = node
  }
  
  insert(value, beforeValue) {
    let pointer = this.headNode;
    
    const node = new Node(value);

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

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

    while(pointer.next) {
      if(pointer.next.value === value) {
        if(pointer.next === this.tailNode) {
          this.tailNode = pointer;
        } else {
          pointer.next = pointer.next.next;
        }
      } 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'); // {'HEAD', null}

const ll = new LinkedList(headNode);

ll.add(new Node(2));
ll.add(new Node(8));
ll.add(new Node(10));
ll.add(new Node(4));
ll.add(new Node(7));

ll.printAll();

ll.remove(7);
ll.add(new Node(33));

ll.printAll();

ll.insert(100, 4);
ll.printAll();

ll.insert(55, 33);
ll.printAll();

ll.add(new Node(1));

ll.printAll();