Vue源码探究之虚拟节点的实现

// 定义并导出VNode类
export default class VNode {
 // 定义实例属性
 tag: string | void; // 标签名称
 data: VNodeData | void; // 节点数据
 children: ?Array<VNode>; // 子虚拟节点列表
 text: string | void; // 节点文字
 elm: Node | void; // 对应DOM节点
 ns: string | void; // 节点命名空间，针对svg标签的属性
 context: Component | void; // rendered in this component's scope // 组件上下文
 key: string | number | void; // 节点唯一键
 componentOptions: VNodeComponentOptions | void; // 虚拟节点组件配置对象
 componentInstance: Component | void; // component instance // 组件实例
 parent: VNode | void; // component placeholder node // 组件占位符节点

 // 严格内部属性，有些属性是服务器渲染的情况使用的，暂时还不了解
 // strictly internal
 // 是否包含原始HTML。只有服务器端会使用
 raw: boolean; // contains raw HTML? (server only) 
 // 是否静态节点，静态节点将会被提升
 isStatic: boolean; // hoisted static node 
 // 是否在根节点插入，进入转换检查所必需的
 isRootInsert: boolean; // necessary for enter transition check
 // 是否空注释占位符
 isComment: boolean; // empty comment placeholder?
 // 是否拷贝节点
 isCloned: boolean; // is a cloned node?
 // 是否一次性节点
 isOnce: boolean; // is a v-once node?
 // 异步组件工厂方法
 asyncFactory: Function | void; // async component factory function
 // 异步源
 asyncMeta: Object | void;
 // 是否异步占位符
 isAsyncPlaceholder: boolean;
 // 服务器端上下文
 ssrContext: Object | void;
 // 功能节点的实际实例上下文
 fnContext: Component | void; // real context vm for functional nodes
 // 方法配置选项，只在服务器渲染使用
 fnOptions: ?ComponentOptions; // for SSR caching
 // 方法作用域id
 fnScopeId: ?string; // functional scope id support

 // 构造函数，参数均可选，与上面定义对应
 constructor (
  tag?: string,
  data?: VNodeData,
  children?: ?Array<VNode>,
  text?: string,
  elm?: Node,
  context?: Component,
  componentOptions?: VNodeComponentOptions,
  asyncFactory?: Function
 ) {
  // 实例初始化赋值
  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
 }

 // 定义child属性的取值器
 // 已弃用：用于向后compat的componentInstance的别名
 // DEPRECATED: alias for componentInstance for backwards compat.
 /* istanbul ignore next */
 get child (): Component | void {
  return this.componentInstance
 }
}

// 定义并导出createEmptyVNode函数，创建空虚拟节点
export const createEmptyVNode = (text: string = '') => {
 // 实例化虚拟节点
 const node = new VNode()
 // 设置节点文字为空，并设置为注释节点
 node.text = text
 node.isComment = true
 // 返回节点
 return node
}

// 定义并导出createTextVNode函数，创建文字虚拟节点
export function createTextVNode (val: string | number) {
 // 置空实例初始化的标签名，数据，子节点属性，只传入文字
 return new VNode(undefined, undefined, undefined, String(val))
}

// 优化浅拷贝
// 用于静态节点和插槽节点，因为它们可以在多个渲染中重用，
// 当DOM操作依赖于它们的elm引用时，克隆它们可以避免错误
// optimized shallow clone
// used for static nodes and slot nodes because they may be reused across
// multiple renders, cloning them avoids errors when DOM manipulations rely
// on their elm reference.
// 定义并导出cloneVNode函数，拷贝节点
export function cloneVNode (vnode: VNode): VNode {
 // 拷贝节点并返回
 const cloned = new VNode(
  vnode.tag,
  vnode.data,
  vnode.children,
  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
}