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;
};