queue - 2

class Queue {
  constructor() {
    this.data = {}
    this.head = 0
    this.tail = 0
  }
  
  enqueue(element) {
    this.data[this.tail] = element
    this.tail++
  }
  
  dequeue() {
    let removed = this.data[this.head]
    delete this.data[this.head]
    this.head++
    return removed
  }
  
  peek() {
    return this.data[this.tail]
  }
  
  isEmpty() {
    return ((this.head - this.tail) === 0)
  }
}