首次加载(更新-元素)

前言

通过patchVnode函数可以对vnode进行更新，对比方式核心就是diff算法

1.创建新元素

• /src/vue/src/core/vdom/patch.ts

function createElm(
  vnode,
  insertedVnodeQueue,
  parentElm?: any,
  refElm?: any,
  nested?: any,
  ownerArray?: any,
  index?: any
) {
  if (isDef(vnode.elm) && isDef(ownerArray)) {
    // This vnode was used in a previous render!
    // now it's used as a new node, overwriting its elm would cause
    // potential patch errors down the road when it's used as an insertion
    // reference node. Instead, we clone the node on-demand before creating
    // associated DOM element for it.
    vnode = ownerArray[index] = cloneVNode(vnode)
  }

  vnode.isRootInsert = !nested // for transition enter check
  if (createComponent(vnode, insertedVnodeQueue, parentElm, refElm)) {
    return
  }

  const data = vnode.data
  const children = vnode.children
  const tag = vnode.tag
  if (isDef(tag)) {
    if (__DEV__) {
      if (data && data.pre) {
        creatingElmInVPre++
      }
      if (isUnknownElement(vnode, creatingElmInVPre)) {
        warn(
          'Unknown custom element: <' +
            tag +
            '> - did you ' +
            'register the component correctly? For recursive components, ' +
            'make sure to provide the "name" option.',
          vnode.context
        )
      }
    }

    vnode.elm = vnode.ns
      ? nodeOps.createElementNS(vnode.ns, tag)
      : nodeOps.createElement(tag, vnode)
    setScope(vnode)

    createChildren(vnode, children, insertedVnodeQueue)
    if (isDef(data)) {
      invokeCreateHooks(vnode, insertedVnodeQueue)
    }
    insert(parentElm, vnode.elm, refElm)

    if (__DEV__ && data && data.pre) {
      creatingElmInVPre--
    }
  } else if (isTrue(vnode.isComment)) {
    vnode.elm = nodeOps.createComment(vnode.text)
    insert(parentElm, vnode.elm, refElm)
  } else {
    vnode.elm = nodeOps.createTextNode(vnode.text)
    insert(parentElm, vnode.elm, refElm)
  }
}

2.将元素插入页面