Implementation of the queue data structure in JavaScript

javascript-queue.js

class Item {
  // stores given value and points to nothing
  constructor (value) {
    this.value = value
    this.next = null
  }
}

class Queue {
  // initial size is 0 and initially just has two reference items that store nothing and point to nothing
  constructor () {
    this.size = 0
    this.front = this.rear = new Item(null)
  }

  // helper function to test
  // prints all items in queue in console
  printItems = () => {
    let item = this.front

    if (item.next) {
      while (item.next !== null) {
        item = item.next
        console.log(item.value)
      }
    } else console.log('Queue empty')
  }

  enqueue = value => {
    // create new node
    let item = new Item(value)

    // make rear item point to new item
    this.rear.next = item

    // new item's point to null anyway so don't need this step
    // item.next = null

    // assign new item as new rear item
    this.rear = item

    this.size++
  }

  dequeue = () => {
    // if no item, return
    if (this.front.next === null) {
      console.log("Queue empty.")
      return null
    }

    // assign first item to temp
    let temp = this.front.next

    // connect front to second item
    this.front.next = temp.next

    // disconnect previous first item from queue
    temp.next = null

    this.size--

    return temp.value
  }

  queueFront = () => {
    // if there's a first item
    if (this.front.next) {
      let firstItem = this.front.next
      return firstItem.value
    } else return null
  }

  isEmpty = () => {
    if (!this.front.next) return true
    else return false
  }

  queueSize = () => {
    return this.size
  }
}


// tests

// const queue = new Queue()
// queue.printItems()

// console.log('size', queue.queueSize())

// queue.enqueue(7)
// queue.enqueue(8)
// queue.enqueue(5)
// queue.printItems()

// console.log('front', queue.queueFront())

// console.log('size', queue.queueSize())

// const removed = queue.dequeue()
// console.log('removed', removed)
// queue.printItems()

// console.log('empty', queue.isEmpty())

// queue.dequeue()

// queue.printItems()
// console.log('empty', queue.isEmpty())
// console.log('front', queue.queueFront())

// queue.dequeue()
// console.log('empty', queue.isEmpty())
// console.log('top', queue.queueFront())

// console.log('size', queue.queueSize())
// console.log('removed', queue.dequeue())