1. VNode

VNode（Virtual Node） 是 Vue 虚拟 DOM 的核心类，用于描述虚拟 DOM 节点的结构和属性。

class VNode {
  tag?: string
  data: VNodeData | undefined
  children?: Array<VNode> | null
  text?: string
  elm: Node | undefined
  ns?: string
  context?: Component // rendered in this component's scope
  key: string | number | undefined
  componentOptions?: VNodeComponentOptions
  componentInstance?: Component // component instance
  parent: VNode | undefined | null // component placeholder node

  // strictly internal
  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?
  isOnce: boolean // is a v-once node?
  asyncFactory?: Function // async component factory function
  asyncMeta: Object | void
  isAsyncPlaceholder: boolean
  ssrContext?: Object | void
  fnContext: Component | void // real context vm for functional nodes
  fnOptions?: ComponentOptions | null // for SSR caching
  devtoolsMeta?: Object | null // used to store functional render context for devtools
  fnScopeId?: string | null // functional scope id support
  isComponentRootElement?: boolean | null // for SSR directives

  constructor(
    tag?: string,
    data?: VNodeData,
    children?: Array<VNode> | null,
    text?: string,
    elm?: Node,
    context?: Component,
    componentOptions?: VNodeComponentOptions,
    asyncFactory?: Function
  ) {
    this.tag = tag
    this.data = data
    this.children = children
    this.text = text
    this.elm = elm
    this.ns = undefined
    this.context = context
    this.fnContext = undefined
    this.fnOptions = undefined
    this.fnScopeId = undefined
    this.key = data && data.key
    this.componentOptions = componentOptions
    this.componentInstance = undefined
    this.parent = undefined
    this.raw = false
    this.isStatic = false
    this.isRootInsert = true
    this.isComment = false
    this.isCloned = false
    this.isOnce = false
    this.asyncFactory = asyncFactory
    this.asyncMeta = undefined
    this.isAsyncPlaceholder = false
  }

  // DEPRECATED: alias for componentInstance for backwards compat.
  /* istanbul ignore next */
  get child(): Component | void {
    return this.componentInstance
  }
}

2.createEmptyVNode

createEmptyVNode 用于创建一个空的 VNode，通常用于表示一个注释节点。

const createEmptyVNode = (text: string = '') => {
  const node = new VNode()
  node.text = text
  node.isComment = true
  return node
}

3.createTextVNode

createTextVNode 用于创建一个文本 VNode，通常用于表示一个文本节点。

function createTextVNode(val: string | number) {
  return new VNode(undefined, undefined, undefined, String(val))
}

4.cloneVNode

cloneVNode 用于克隆一个 VNode，通常用于创建一个克隆节点。

function cloneVNode(vnode: VNode): VNode {
  const cloned = new VNode(
    vnode.tag,
    vnode.data,
    // #7975
    // clone children array to avoid mutating original in case of cloning
    // a child.
    vnode.children && vnode.children.slice(),
    vnode.text,
    vnode.elm,
    vnode.context,
    vnode.componentOptions,
    vnode.asyncFactory
  )
  cloned.ns = vnode.ns
  cloned.isStatic = vnode.isStatic
  cloned.key = vnode.key
  cloned.isComment = vnode.isComment
  cloned.fnContext = vnode.fnContext
  cloned.fnOptions = vnode.fnOptions
  cloned.fnScopeId = vnode.fnScopeId
  cloned.asyncMeta = vnode.asyncMeta
  cloned.isCloned = true
  return cloned
}