哈喽,大家好,接着上回的,我们继续一起学习吧!
根据昨天的学习,我们知道运用了virtual DOM和diff算法,可以提高程序性能,那么我们今天开始就要看看到底是怎么提高性能的。
diff算法核心思想是:
diff的实现过程是patch(container,vnode)和patch(vnode,newVnode);
diff的实现的核心是createElement和updateChildren.
下面我们来看一些patch都干了什么:
/*createPatchFunction的返回值,一个patch函数*/
return function patch (oldVnode, vnode, hydrating, removeOnly, parentElm, refElm) {
/*vnode不存在则直接调用销毁钩子*/
if (isUndef(vnode)) {
if (isDef(oldVnode)) invokeDestroyHook(oldVnode)
return
}
let isInitialPatch = false
const insertedVnodeQueue = []
if (isUndef(oldVnode)) {
// empty mount (likely as component), create new root element
/*oldVnode未定义的时候,其实也就是root节点,创建一个新的节点*/
isInitialPatch = true
createElm(vnode, insertedVnodeQueue, parentElm, refElm)
} else {
/*标记旧的VNode是否有nodeType*/
/*Github:https://github.com/answershuto*/
const isRealElement = isDef(oldVnode.nodeType)
if (!isRealElement && sameVnode(oldVnode, vnode)) {
// patch existing root node
/*是同一个节点的时候直接修改现有的节点*/
patchVnode(oldVnode, vnode, insertedVnodeQueue, removeOnly)
} else {
if (isRealElement) {
// mounting to a real element
// check if this is server-rendered content and if we can perform
// a successful hydration.
if (oldVnode.nodeType === 1 && oldVnode.hasAttribute(SSR_ATTR)) {
/*当旧的VNode是服务端渲染的元素,hydrating记为true*/
oldVnode.removeAttribute(SSR_ATTR)
hydrating = true
}
if (isTrue(hydrating)) {
/*需要合并到真实DOM上*/
if (hydrate(oldVnode, vnode, insertedVnodeQueue)) {
/*调用insert钩子*/
invokeInsertHook(vnode, insertedVnodeQueue, true)
return oldVnode
} else if (process.env.NODE_ENV !== 'production') {
warn(
'The client-side rendered virtual DOM tree is not matching ' +
'server-rendered content. This is likely caused by incorrect ' +
'HTML markup, for example nesting block-level elements inside ' +
'<p>, or missing <tbody>. Bailing hydration and performing ' +
'full client-side render.'
)
}
}
// either not server-rendered, or hydration failed.
// create an empty node and replace it
/*如果不是服务端渲染或者合并到真实DOM失败,则创建一个空的VNode节点替换它*/
oldVnode = emptyNodeAt(oldVnode)
}
// replacing existing element
/*取代现有元素*/
const oldElm = oldVnode.elm
const parentElm = nodeOps.parentNode(oldElm)
createElm(
vnode,
insertedVnodeQueue,
// extremely rare edge case: do not insert if old element is in a
// leaving transition. Only happens when combining transition +
// keep-alive + HOCs. (#4590)
oldElm._leaveCb ? null : parentElm,
nodeOps.nextSibling(oldElm)
)
if (isDef(vnode.parent)) {
// component root element replaced.
// update parent placeholder node element, recursively
/*组件根节点被替换,遍历更新父节点element*/
let ancestor = vnode.parent
while (ancestor) {
ancestor.elm = vnode.elm
ancestor = ancestor.parent
}
if (isPatchable(vnode)) {
/*调用create回调*/
for (let i = 0; i < cbs.create.length; ++i) {
cbs.create[i](emptyNode, vnode.parent)
}
}
}
if (isDef(parentElm)) {
/*移除老节点*/
removeVnodes(parentElm, [oldVnode], 0, 0)
} else if (isDef(oldVnode.tag)) {
/*Github:https://github.com/answershuto*/
/*调用destroy钩子*/
invokeDestroyHook(oldVnode)
}
}
}
/*调用insert钩子*/
invokeInsertHook(vnode, insertedVnodeQueue, isInitialPatch)
return vnode.elm
}
从上面的代码来看patch主要做了:
以上最重要的是第三步,怎么判断新旧几点是不是同一节点呢???预知后事,请听下回分解。
if (isDef(parentElm)) {
/*移除老节点*/
removeVnodes(parentElm, [oldVnode], 0, 0)
} else if (isDef(oldVnode.tag)) {
/*Github:https://github.com/answershuto*/
/*调用destroy钩子*/
invokeDestroyHook(oldVnode)
}
最后这里我没看懂,不知道parentElm是啥,之后看懂了告诉你哈。
愿我们有能力不向生活缴械投降---Lin
参考文档:https://blog.csdn.net/github_36546211/article/details/78023747