with head

linkedlist.js

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

// {value, next}

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

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

    while(pointer.next) {
      pointer = pointer.next;
    }
    
    pointer.next = node;
  }
  
  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;
        pointer.next = node;
      }
    }                   
  }
  
  remove(value) {
    let pointer = this.headNode;

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

    while(pointer.next) {
      pointer = pointer.next;
      console.log(pointer.value);      
    }               
  }
}


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(2);

ll.printAll();

ll.insert(100, 4);
ll.insert(55, 7);

ll.printAll();