队列的实现，先进先出 FIFO（First in、First out）

[qiuhongbingo]

class Queue {
  constructor(...args) {
    this.queue = [...args]
  }

  enqueue(...items) {
    return this.queue.push(...items)
  }

  dequeue() {
    return this.queue.shift()
  }

  front() {
    return this.isEmpty() ? undefined : this.queue[0]
  }

  back() {
    return this.isEmpty() ? undefined : this.queue[this.size() - 1]
  }

  isEmpty() {
    return this.size() == 0
  }

  size() {
    return this.queue.length
  }
}