Implementation of a Queue with the help of stacks in JavaScript

QueueWithStack.js

class Stack {
  constructor(size) {
    this.size = size
    this._stack = []
  }
  
  push(val) {
    if(this._stack.length > this.size) {
       return 
  	}
    this._stack = [val, ...this._stack]
    return val
  }
  pop() {
    if(!this._stack.length) {
      return
    }
    const out = this._stack[0]
    this._stack = this._stack.splice(1)
    return out
  }
  empty() {
    this._stack = []
  }
  count() {
    return this._stack.length
  }
}


class QueueWithStack {
  constructor(size) {
    this._queue1 = new Stack(size)
    this._queue2 = new Stack(size)
    this.size = size
  }
  enqueue(val) {
    if(this._queue1.count() >= this.size) {
      return
    }
    this._queue2.push(val)
    let queue1Val = this._queue1.pop()
    while(queue1Val) {
      this._queue2.push(queue1Val)
      queue1Val = this._queue1.pop()
    }
    let queue2Val = this._queue2.pop()
    while(queue2Val) {
      this._queue1.push(queue2Val)
      queue2Val = this._queue2.pop()
    }
    this._queue2.empty()
    return val
  }
  dequeue() {
    if(!this._queue1.count()) {
       return 
  	}
    let queue1Val = this._queue1.pop()
    while(queue1Val) {
      this._queue2.push(queue1Val)
      queue1Val = this._queue1.pop()
    }
    const out = this._queue2.pop()
    let queue2Val = this._queue2.pop()
    while(queue2Val) {
      this._queue1.push(queue2Val)
      queue2Val = this._queue2.pop()
    }
    this._queue2.empty()
    return out
  }
}

const queue = new QueueWithStack(3)
queue.enqueue(1)
queue.enqueue(2)
queue.enqueue(3)
queue.dequeue()
queue.dequeue()