前言
1.什么是 diff
diff 算法是一种通过同层的树节点进行比拟的高效算法
2.diff 具备哪些劣势
比拟只会在同层级进行, 不会跨层级比拟。在 diff 比拟的过程中，循环从两边向两头比拟
diff 流程图
patch
github: vuejs/vue@2.6.14 patch
/** * 是否是 非空 */function isUndef(v: any) { return v === undefined || v === null;}/** * 是否不是 非空 */function isDef(v: any) { return v !== undefined && v !== null;}/** * * @param oldVnode * @param vnode * @param hydrating * @param removeOnly */function patch(oldVnode, vnode, hydrating, removeOnly) { // 如果 新vnode 不存在 if (isUndef(vnode)) { // 如果 老vnode 存在， if (isDef(oldVnode)) invokeDestroyHook(oldVnode); return; } let isInitialPatch = false; const insertedVnodeQueue = []; // 老vnode不存在（首次渲染） if (isUndef(oldVnode)) { isInitialPatch = true; createElm(vnode, insertedVnodeQueue); } // 更新节点阶段 else { const isRealElement = isDef(oldVnode.nodeType); // 不是实在节点，并且 新、老节点是同一节点 if (!isRealElement && sameVnode(oldVnode, vnode)) { // 进行更新节点 patchVnode(oldVnode, vnode, insertedVnodeQueue, null, null, removeOnly); } else { if (isRealElement) { // 是否是 ssr渲染 if (oldVnode.nodeType === 1 && oldVnode.hasAttribute(SSR_ATTR)) { oldVnode.removeAttribute(SSR_ATTR); hydrating = true; } // ssr渲染逻辑 if (isTrue(hydrating)) { // 混合 if (hydrate(oldVnode, vnode, insertedVnodeQueue)) { 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.' ); } } // 不是 ssr渲染或混合失败，则创立一个空节点 oldVnode = emptyNodeAt(oldVnode); } // replacing existing element const oldElm = oldVnode.elm; const parentElm = nodeOps.parentNode(oldElm); // create new node 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) ); // update parent placeholder node element, recursively if (isDef(vnode.parent)) { let ancestor = vnode.parent; const patchable = isPatchable(vnode); // 遍历 父节点 while (ancestor) { // 卸载老节点的所有组件 for (let i = 0; i < cbs.destroy.length; ++i) { cbs.destroy[i](ancestor); } // 替换节点 ancestor.elm = vnode.elm; if (patchable) { for (let i = 0; i < cbs.create.length; ++i) { cbs.create[i](emptyNode, ancestor); } // #6513 // invoke insert hooks that may have been merged by create hooks. // e.g. for directives that uses the "inserted" hook. const insert = ancestor.data.hook.insert; if (insert.merged) { // start at index 1 to avoid re-invoking component mounted hook for (let i = 1; i < insert.fns.length; i++) { insert.fns[i](); } } } else { registerRef(ancestor); } // 更新父节点 ancestor = ancestor.parent; } } // 如果老节点存在，则删除 if (isDef(parentElm)) { removeVnodes([oldVnode], 0, 0); } // 否则卸载 老节点 else if (isDef(oldVnode.tag)) { invokeDestroyHook(oldVnode); } } } // 注册节点 invokeInsertHook(vnode, insertedVnodeQueue, isInitialPatch); return vnode.elm;}sameVnode
判断是否是同一个节点
github: vuejs/vue@2.6.14 sameVnode
/** * 比拟节点是否雷同 */function sameVnode(a, b) { return ( // 比拟 key 是否雷同 a.key === b.key && // 比拟是不是都是异步组件 a.asyncFactory === b.asyncFactory && // 比拟标签名称是否雷同 ((a.tag === b.tag && // 解析代码后，比拟是否都是被正文后的节点 a.isComment === b.isComment && // 比拟 data 数据援用是否雷同 isDef(a.data) === isDef(b.data) && // 比拟 input 标签的 data、attrs、type 是否雷同 sameInputType(a, b)) || // (isTrue(a.isAsyncPlaceholder) && isUndef(b.asyncFactory.error))) );}sameVnode 函数应用到的工具类
/** * 判断a和b若input，则是否雷同 */function sameInputType(a, b) { // 不比拟非 input 标签 if (a.tag !== 'input') return true; let i; // 判断 data、attrs、type 属性是否非空 const typeA = isDef((i = a.data)) && isDef((i = i.attrs)) && i.type; const typeB = isDef((i = b.data)) && isDef((i = i.attrs)) && i.type; // 判断 a 和 b 都不是非空，并且判断 input type 属性是否正确 return typeA === typeB || (isTextInputType(typeA) && isTextInputType(typeB));}/** * 宰割 str 字符串，通过闭包判断 key 字段是否命中内容 */function makeMap(str: string, expectsLowerCase?: boolean): (key: string) => true | void { const map = Object.create(null); const list: Array<string> = str.split(','); for (let i = 0; i < list.length; i++) { map[list[i]] = true; } return expectsLowerCase ? (val) => map[val.toLowerCase()] : (val) => map[val];}/** * input 属性为 输出类型的 type 值 */const isTextInputType = makeMap('text,number,password,search,email,tel,url');/** * 是否为 true */function isTrue(v: any): boolean %checks { return v === true;}patchVnode
github: vuejs/vue@2.6.14 patchVnode
/** * 给 vnode 打补丁 * @param oldVnode 老虚构dom节点 * @param vnode 新虚构dom节点 * @param insertedVnodeQueue * @param ownerArray * @param index * @param removeOnly */function patchVnode(oldVnode, vnode, insertedVnodeQueue, ownerArray, index, removeOnly) { // 若新节点和老节点援用雷同，则跳过 if (oldVnode === vnode) { return; } // if (isDef(vnode.elm) && isDef(ownerArray)) { // clone reused vnode vnode = ownerArray[index] = cloneVNode(vnode); } const elm = (vnode.elm = oldVnode.elm); if (isTrue(oldVnode.isAsyncPlaceholder)) { if (isDef(vnode.asyncFactory.resolved)) { hydrate(oldVnode.elm, vnode, insertedVnodeQueue); } else { vnode.isAsyncPlaceholder = true; } return; } // 新、老节点都是动态节点，且 key 都雷同，并新的vnode是克隆节点或绑定了 v-once, 则赋值后完结 if ( isTrue(vnode.isStatic) && isTrue(oldVnode.isStatic) && vnode.key === oldVnode.key && (isTrue(vnode.isCloned) || isTrue(vnode.isOnce)) ) { vnode.componentInstance = oldVnode.componentInstance; return; } // hook let i; const data = vnode.data; if (isDef(data) && isDef((i = data.hook)) && isDef((i = i.prepatch))) { i(oldVnode, vnode); } const oldCh = oldVnode.children; const ch = vnode.children; if (isDef(data) && isPatchable(vnode)) { for (i = 0; i < cbs.update.length; ++i) cbs.update[i](oldVnode, vnode); if (isDef((i = data.hook)) && isDef((i = i.update))) i(oldVnode, vnode); } // 如果新vnode没有 文本内容，则代表可能有子节点 if (isUndef(vnode.text)) { // 如果新、老节点都有子节点 if (isDef(oldCh) && isDef(ch)) { // 如果子节点不雷同，则更新节点 if (oldCh !== ch) updateChildren(elm, oldCh, ch, insertedVnodeQueue, removeOnly); } // 新vnode的子节点非空 else if (isDef(ch)) { // 开发环境，查看新节点的子节点是否存在反复key，如有则console抛出正告提醒 if (process.env.NODE_ENV !== 'production') { checkDuplicateKeys(ch); } // if (isDef(oldVnode.text)) nodeOps.setTextContent(elm, ''); addVnodes(elm, null, ch, 0, ch.length - 1, insertedVnodeQueue); } // 如果新节点没有子节点，但老节点有子节点，则删除老节点的子节点 else if (isDef(oldCh)) { removeVnodes(oldCh, 0, oldCh.length - 1); } // 如果老节点的本人就是 文本内容，则清空 else if (isDef(oldVnode.text)) { nodeOps.setTextContent(elm, ''); } } // 如果新老节点的 文本内容不雷同，则更新 新节点 文本内容 else if (oldVnode.text !== vnode.text) { nodeOps.setTextContent(elm, vnode.text); } if (isDef(data)) { if (isDef((i = data.hook)) && isDef((i = i.postpatch))) i(oldVnode, vnode); }}updateChildren
github: vuejs/vue@2.6.14 updateChildren
/** * @param parentElm * @param oldCh * @param newCh * @param insertedVnodeQueue * @param removeOnly */function updateChildren(parentElm, oldCh, newCh, insertedVnodeQueue, removeOnly) { let oldStartIdx = 0; let newStartIdx = 0; let oldEndIdx = oldCh.length - 1; let oldStartVnode = oldCh[0]; let oldEndVnode = oldCh[oldEndIdx]; let newEndIdx = newCh.length - 1; let newStartVnode = newCh[0]; let newEndVnode = newCh[newEndIdx]; let oldKeyToIdx, idxInOld, vnodeToMove, refElm; // removeOnly is a special flag used only by <transition-group> // to ensure removed elements stay in correct relative positions // during leaving transitions const canMove = !removeOnly; if (process.env.NODE_ENV !== 'production') { checkDuplicateKeys(newCh); } while (oldStartIdx <= oldEndIdx && newStartIdx <= newEndIdx) { // if (isUndef(oldStartVnode)) { oldStartVnode = oldCh[++oldStartIdx]; // Vnode has been moved left } // else if (isUndef(oldEndVnode)) { oldEndVnode = oldCh[--oldEndIdx]; } // 新老节点 头头比拟 else if (sameVnode(oldStartVnode, newStartVnode)) { patchVnode(oldStartVnode, newStartVnode, insertedVnodeQueue, newCh, newStartIdx); oldStartVnode = oldCh[++oldStartIdx]; newStartVnode = newCh[++newStartIdx]; } // 新老节点 尾尾比拟 else if (sameVnode(oldEndVnode, newEndVnode)) { patchVnode(oldEndVnode, newEndVnode, insertedVnodeQueue, newCh, newEndIdx); oldEndVnode = oldCh[--oldEndIdx]; newEndVnode = newCh[--newEndIdx]; } // 新老节点 尾头比拟 else if (sameVnode(oldStartVnode, newEndVnode)) { // Vnode moved right patchVnode(oldStartVnode, newEndVnode, insertedVnodeQueue, newCh, newEndIdx); canMove && nodeOps.insertBefore( parentElm, oldStartVnode.elm, nodeOps.nextSibling(oldEndVnode.elm) ); oldStartVnode = oldCh[++oldStartIdx]; newEndVnode = newCh[--newEndIdx]; } // 新老节点 头尾比拟 else if (sameVnode(oldEndVnode, newStartVnode)) { // Vnode moved left patchVnode(oldEndVnode, newStartVnode, insertedVnodeQueue, newCh, newStartIdx); canMove && nodeOps.insertBefore(parentElm, oldEndVnode.elm, oldStartVnode.elm); oldEndVnode = oldCh[--oldEndIdx]; newStartVnode = newCh[++newStartIdx]; } // else { if (isUndef(oldKeyToIdx)) oldKeyToIdx = createKeyToOldIdx(oldCh, oldStartIdx, oldEndIdx); idxInOld = isDef(newStartVnode.key) ? oldKeyToIdx[newStartVnode.key] : findIdxInOld(newStartVnode, oldCh, oldStartIdx, oldEndIdx); if (isUndef(idxInOld)) { // New element createElm( newStartVnode, insertedVnodeQueue, parentElm, oldStartVnode.elm, false, newCh, newStartIdx ); } else { vnodeToMove = oldCh[idxInOld]; if (sameVnode(vnodeToMove, newStartVnode)) { patchVnode(vnodeToMove, newStartVnode, insertedVnodeQueue, newCh, newStartIdx); oldCh[idxInOld] = undefined; canMove && nodeOps.insertBefore(parentElm, vnodeToMove.elm, oldStartVnode.elm); } else { // same key but different element. treat as new element createElm( newStartVnode, insertedVnodeQueue, parentElm, oldStartVnode.elm, false, newCh, newStartIdx ); } } newStartVnode = newCh[++newStartIdx]; } } if (oldStartIdx > oldEndIdx) { refElm = isUndef(newCh[newEndIdx + 1]) ? null : newCh[newEndIdx + 1].elm; addVnodes(parentElm, refElm, newCh, newStartIdx, newEndIdx, insertedVnodeQueue); } else if (newStartIdx > newEndIdx) { removeVnodes(oldCh, oldStartIdx, oldEndIdx); }}