vue源码中属性旁边的?和|是什么意思

Question

比如下面这个里面的？和|，是es6里面的吗，可是我看es6没看到哇？

export default class VNode {
  tag: string | void;
  data: VNodeData | void;
  children: Array<VNode> | void;
  text: string | void;
  elm: Node | void;
  ns: string | void;
  context: Component | void; // rendered in this component's scope
  key: string | number | void;
  componentOptions: VNodeComponentOptions | void;
  child: Component | void; // component instance
  parent: VNode | void; // compoennt placeholder node
  raw: boolean; // contains raw HTML? (server only)
  isStatic: boolean; // hoisted static node
  isRootInsert: boolean; // necessary for enter transition check
  isComment: boolean; // empty comment placeholder?
  isCloned: boolean; // is a cloned node?

  constructor (
    tag?: string,
    data?: VNodeData,
    children?: Array<VNode> | void,
    text?: string,
    elm?: Node,
    ns?: string | void,
    context?: Component,
    componentOptions?: VNodeComponentOptions
  ) {
    this.tag = tag
    this.data = data
    this.children = children
    this.text = text
    this.elm = elm
    this.ns = ns
    this.context = context
    this.key = data && data.key
    this.componentOptions = componentOptions
    this.child = undefined
    this.parent = undefined
    this.raw = false
    this.isStatic = false
    this.isRootInsert = true
    this.isComment = false
    this.isCloned = false
  }
}

还有下面这种？又在后面了

type PropOptions = {
  type: Function | Array<Function> | null,
  default: any,
  required: ?boolean,
  validator: ?Function
}

Answer 1

这个不是es6，是flow，一个类型检查、分析工具

type: Function | Array<Function> | null,： 表示，type可能是Function，也可能是Array of Function，还可能是null

required: ?boolean,： 表示required是个可选参数，类型是boolean