See: https://codesandbox.io/s/billowing-haze-06yv62?file=%2Fsrc%2Findex.js%3A0-1782

SinglyLinkedList.js

class SinglyLinkedListNode {
  constructor(value) {
    this.value = value;
    this.tail = null;
  }

  valueOf() {
    return this.value;
  }
}

class SinglyLinkedList {
  constructor(values = []) {
    this.head = null;
    this.length = 0;

    for (const value of values) {
      this.push(value);
    }
  }

  unshift(value) {
    const node = new SinglyLinkedListNode(value);

    const currentHead = this.head;
    node.tail = currentHead;
    this.head = node;

    this.length++;
  }

  shift() {
    const currentHead = this.head;
    const value = currentHead ? currentHead.value : null;

    this.head = currentHead.tail;
    this.length--;

    return value;
  }

  push(value) {
    const node = new SinglyLinkedListNode(value);

    if (!this.head) {
      this.head = node;

      this.length++;
      return;
    }

    let currentNode = this.head;
    while (currentNode.tail) {
      currentNode = currentNode.tail;
    }
    currentNode.tail = node;

    this.length++;
  }

  pop() {
    if (!this.head) {
      return null;
    }

    let currentNode = this.head;
    while (currentNode.tail) {
      if (currentNode.tail && !currentNode.tail.tail) {
        const value = currentNode.tail.value;
        currentNode.tail = null;
        this.length--;
        return value;
      }
      currentNode = currentNode.tail;
    }
  }

  *[Symbol.iterator]() {
    let currentNode = this.head;
    if (!currentNode) {
      return;
    }

    while (currentNode) {
      yield currentNode.value;
      currentNode = currentNode.tail;
    }
  }
}

const list = new SinglyLinkedList([-2, -1, 0]);
list.push(1);
list.push(2);
list.push(3);
list.pop();
list.push(3);
for (let v of list) {
  console.log(v);
}

console.log(list);

See also: DoublyLinkedList.js

See reverse: https://codesandbox.io/s/distracted-banach-t7ds8z?file=%2Fsrc%2Findex.js%3A0-2149

Note: this actually consumes the list right now, which you might not want tbh.

function reverse(ll) {
  let currentNode = ll.tail;
  if (!currentNode) {
    return;
  }

  let previousNode = null;
  while (currentNode) {
    [currentNode.tail, previousNode, currentNode] = [
      previousNode,
      currentNode,
      currentNode.tail
    ];
  }

  const rll = new SinglyLinkedList();
  rll.tail = previousNode;

  return rll;
}

See also, my attempt to use less variables.