Stack using Queue

file.js

class Stack {
  constructor() {
    this._queue = new Queue();
    this._size = 0;
  }
  
  push(val) {
    this._queue.enqueue(val)
  }
  
  pop() {
    if (this._size == 0) {
      return null;
    }
    
    for (let i = 0; i < this._size - 1; i++) {
      this._queue.enqueue(this._queue.dequeue())
    }
    
    this._size--;
    
    return this._queue.dequeue();
  } 
}