// @returns {VNode}
createElement(
  // {String | Object | Function}
  // 一個(gè) HTML 標(biāo)簽名、組件選項(xiàng)對(duì)象，或者
  // resolve 了上述任何一種的一個(gè) async 函數(shù)。必填項(xiàng)。
  'div',

  // {Object}
  // 一個(gè)與模板中屬性對(duì)應(yīng)的數(shù)據(jù)對(duì)象。可選。
  {
    // (詳情見(jiàn)下一節(jié))
  },

  // {String | Array}
  // 子級(jí)虛擬節(jié)點(diǎn) (VNodes)，由 `createElement()` 構(gòu)建而成，
  // 也可以使用字符串來(lái)生成“文本虛擬節(jié)點(diǎn)”。可選。
  [
    '先寫(xiě)一些文字',
    createElement('h1', '一則頭條'),
    createElement(MyComponent, {
      props: {
        someProp: 'foobar'
      }
    })
  ]
)

//創(chuàng)建一個(gè)div節(jié)點(diǎn)
createElement("div", {
	 return createElement("div", {
        domProps: {
          innerHTML: "hello !"
        }
      })
})
// 按照組件名來(lái)返回一個(gè)虛擬dom
createElement("component-name", {
   props: {
      name: "hello"
  }
}）

//  設(shè)置子對(duì)象
return createElement("div", {
     class: "box"
}, [
   createElement("span", {
     domProps: {
           innerHTML: 'bob !'
     }
   })
 ])

function _createElement (
    context,
    tag,
    data,
    children,
    normalizationType
  ) {
    if (isDef(data) && isDef((data).__ob__)) { //檢測(cè)是否是響應(yīng)式數(shù)據(jù)
      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)) { //檢測(cè)data中是否有is屬性，是的話(huà)tag替換為is指向的內(nèi)容，處理動(dòng)態(tài)組件
      tag = data.is;
    }
    if (!tag) { // tag如果為空，創(chuàng)建空虛擬節(jié)點(diǎn)
      // 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如果定義了必須是數(shù)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;
    }
    // 標(biāo)準(zhǔn)化處理children的兩種模式
    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)) { // 判讀是否是標(biāo)準(zhǔn)的html 標(biāo)簽
        // 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對(duì)應(yīng)的是組件名，創(chuàng)建組件
        // 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;
  };