Vue 中 createElement 使用实例详解

// @returns {VNode}
createElement(
  // {String | Object | Function}
  // 一个 HTML 标签名、组件选项对象，或者
  // resolve 了上述任何一种的一个 async 函数。必填项。
  'div',

  // {Object}
  // 一个与模板中属性对应的数据对象。可选。
  {
    // (详情见下一节)
  },

  // {String | Array}
  // 子级虚拟节点 (VNodes)，由 `createElement()` 构建而成，
  // 也可以使用字符串来生成“文本虚拟节点”。可选。
  [
    '先写一些文字',
    createElement('h1', '一则头条'),
    createElement(MyComponent, {
      props: {
        someProp: 'foobar'
      }
    })
  ]
)

//创建一个div节点
createElement("div", {
	 return createElement("div", {
        domProps: {
          innerHTML: "hello !"
        }
      })
})
// 按照组件名来返回一个虚拟dom
createElement("component-name", {
   props: {
      name: "hello"
  }
}）

//  设置子对象
return createElement("div", {
     class: "box"
}, [
   createElement("span", {
     domProps: {
           innerHTML: 'bob !'
     }
   })
 ])

function _createElement (
    context,
    tag,
    data,
    children,
    normalizationType
  ) {
    if (isDef(data) && isDef((data).__ob__)) { //检测是否是响应式数据
      warn(
        "Avoid using observed data object as vnode data: " + (JSON.stringify(data)) + "\n" +
        'Always create fresh vnode data objects in each render!',
        context
      );
      return createEmptyVNode()
    }
    // object syntax in v-bind
    if (isDef(data) && isDef(data.is)) { //检测data中是否有is属性，是的话tag替换为is指向的内容，处理动态组件
      tag = data.is;
    }
    if (!tag) { // tag如果为空，创建空虚拟节点
      // in case of component :is set to falsy value
      return createEmptyVNode()
    }
    // warn against non-primitive key
    if (isDef(data) && isDef(data.key) && !isPrimitive(data.key) // data 中的key如果定义了必须是数字或者字符串
    ) {
      {
        warn(
          'Avoid using non-primitive value as key, ' +
          'use string/number value instead.',
          context
        );
      }
    }
    // support single function children as default scoped slot
    if (Array.isArray(children) &&
      typeof children[0] === 'function'
    ) {
      data = data || {};
      data.scopedSlots = { default: children[0] };
      children.length = 0;
    }
    // 标准化处理children的两种模式
    if (normalizationType === ALWAYS_NORMALIZE) {
      children = normalizeChildren(children);
    } else if (normalizationType === SIMPLE_NORMALIZE) {
      children = simpleNormalizeChildren(children);
    }
    var vnode, ns;
    if (typeof tag === 'string') {
      var Ctor;
      ns = (context.$vnode && context.$vnode.ns) || config.getTagNamespace(tag);
      if (config.isReservedTag(tag)) { // 判读是否是标准的html 标签
        // platform built-in elements
        vnode = new VNode(
          config.parsePlatformTagName(tag), data, children,
          undefined, undefined, context
        );
      } else if ((!data || !data.pre) && isDef(Ctor = resolveAsset(context.$options, 'components', tag))) {// 如果tag对应的是组件名，创建组件
        // component
        vnode = createComponent(Ctor, data, context, children, tag);
      } else {
        // unknown or unlisted namespaced elements
        // check at runtime because it may get assigned a namespace when its
        // parent normalizes children
        vnode = new VNode(
          tag, data, children,
          undefined, undefined, context
        );
      }
    } else {
      // direct component options / constructor
      vnode = createComponent(tag, data, context, children);
    }
    if (Array.isArray(vnode)) {
      return vnode
    } else if (isDef(vnode)) {
      if (isDef(ns)) { applyNS(vnode, ns); }
      if (isDef(data)) { registerDeepBindings(data); }
      return vnode
    } else {
      return createEmptyVNode()
    }
  }

var VNode = function VNode (
    tag,
    data,
    children,
    text,
    elm,
    context,
    componentOptions,
    asyncFactory
  ) {
    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;
  };