栈的实现，后进先出 LIFO（Last in、First out）

[qiuhongbingo]

class Stack {
  constructor(...args) {
    this.stack = [...args]
  }

  push(...items) {
    return this.stack.push(...items)
  }

  pop() {
    return this.stack.pop()
  }

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

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

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