This time I will bring you a summary of the techniques for using the diff algorithm. What are the precautions when using the diff algorithm? The following is a practical case, let’s take a look.
Virtual dom
The diff algorithm must first clarify the concept that the object of diff is the virtual dom, and updating the real dom is the result of the diff algorithm
Vnode base class
constructor ( 。。。 ) { 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 }
This part of the code is mainly to better understand the meaning of the attribute of the specific diff in the diff algorithm. Of course, it can also be better understood Understand the vnode instance
The overall process
The core function is the patch function
isUndef judgment (whether it is undefined or null)
// empty mount (likely as component), create new root elementcreateElm(vnode, insertedVnodeQueue) Here you can find that creating nodes is not inserted one by one, but put into a queue for unified batch processing
Core function sameVnode
function sameVnode (a, b) { return ( a.key === b.key && ( ( a.tag === b.tag && a.isComment === b.isComment && isDef(a.data) === isDef(b.data) && sameInputType(a, b) ) || ( isTrue(a.isAsyncPlaceholder) && a.asyncFactory === b.asyncFactory && isUndef(b.asyncFactory.error) ) ) ) }
Here is an outer comparison function that directly compares the keys and tags of the two nodes. ), compare data (note that data here refers to VNodeData), and directly compare types for input.
export interface VNodeData { key?: string | number; slot?: string; scopedSlots?: { [key: string]: ScopedSlot }; ref?: string; tag?: string; staticClass?: string; class?: any; staticStyle?: { [key: string]: any }; style?: object[] | object; props?: { [key: string]: any }; attrs?: { [key: string]: any }; domProps?: { [key: string]: any }; hook?: { [key: string]: Function }; on?: { [key: string]: Function | Function[] }; nativeOn?: { [key: string]: Function | Function[] }; transition?: object; show?: boolean; inlineTemplate?: { render: Function; staticRenderFns: Function[]; }; directives?: VNodeDirective[]; keepAlive?: boolean; }
This will confirm whether the two nodes have further comparison value, otherwise they will be replaced directly
The replacement process is mainly a createElm function and the other is to destroy the oldVNode
// destroy old node if (isDef(parentElm)) { removeVnodes(parentElm, [oldVnode], 0, 0) } else if (isDef(oldVnode.tag)) { invokeDestroyHook(oldVnode) }
Insert To simplify the process, it is to determine the type of the node and call
createComponent respectively (it will determine whether there are children and then call it recursively)
createComment
createTextNode
After creation After using the insert function
, you need to use the hydrate function to map the virtual dom and the real dom
function insert (parent, elm, ref) { if (isDef(parent)) { if (isDef(ref)) { if (ref.parentNode === parent) { nodeOps.insertBefore(parent, elm, ref) } } else { nodeOps.appendChild(parent, elm) } } }
Core function
function patchVnode (oldVnode, vnode, insertedVnodeQueue, removeOnly) { if (oldVnode === vnode) { return } 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 } if (isTrue(vnode.isStatic) && isTrue(oldVnode.isStatic) && vnode.key === oldVnode.key && (isTrue(vnode.isCloned) || isTrue(vnode.isOnce)) ) { vnode.componentInstance = oldVnode.componentInstance return } 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) } if (isUndef(vnode.text)) { if (isDef(oldCh) && isDef(ch)) { if (oldCh !== ch) updateChildren(elm, oldCh, ch, insertedVnodeQueue, removeOnly) } else if (isDef(ch)) { if (isDef(oldVnode.text)) nodeOps.setTextContent(elm, '') addVnodes(elm, null, ch, 0, ch.length - 1, insertedVnodeQueue) } else if (isDef(oldCh)) { removeVnodes(elm, oldCh, 0, oldCh.length - 1) } else if (isDef(oldVnode.text)) { nodeOps.setTextContent(elm, '') } } 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) } }
const el = vnode.el = oldVnode.el This is a very important step. Let vnode.el refer to the current real dom. When el is modified, vnode.el will change synchronously.
Compare whether the two references are consistent
I don’t know what asyncFactory does after that, so I can’t understand this comparison
Static node comparison key, no re-rendering will be done after the same, directly copy componentInstance (once command takes effect here)
If vnode is a text node Or Comment node, but when vnode.text != oldVnode.text, you only need to update the text content of vnode.elm
Comparison of children
If only oldVnode has child nodes, then delete these nodes
If only vnode has child nodes, then delete them Create these child nodes. If oldVnode is a text node, set the text of vnode.elm to empty String
If both are present, updateChildren will be updated. This will be detailed later.
If neither oldVnode nor vnode has child nodes, but oldVnode is a text node or comment node, set the text of vnode.elm to an empty string
updateChildren
This part focuses on the entire algorithm
First four pointers, oldStart, oldEnd, newStart, newEnd, two arrays, oldVnode, Vnode .
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 while (oldStartIdx <= oldEndIdx && newStartIdx <= newEndIdx) { if (isUndef(oldStartVnode)) { oldStartVnode = oldCh[++oldStartIdx] // Vnode has been moved left } else if (isUndef(oldEndVnode)) { oldEndVnode = oldCh[--oldEndIdx] } else if (sameVnode(oldStartVnode, newStartVnode)) { patchVnode(oldStartVnode, newStartVnode, insertedVnodeQueue) oldStartVnode = oldCh[++oldStartIdx] newStartVnode = newCh[++newStartIdx] } else if (sameVnode(oldEndVnode, newEndVnode)) { patchVnode(oldEndVnode, newEndVnode, insertedVnodeQueue) oldEndVnode = oldCh[--oldEndIdx] newEndVnode = newCh[--newEndIdx] } else if (sameVnode(oldStartVnode, newEndVnode)) { // Vnode moved right patchVnode(oldStartVnode, newEndVnode, insertedVnodeQueue) canMove && nodeOps.insertBefore(parentElm, oldStartVnode.elm, nodeOps.nextSibling(oldEndVnode.elm)) oldStartVnode = oldCh[++oldStartIdx] newEndVnode = newCh[--newEndIdx] } else if (sameVnode(oldEndVnode, newStartVnode)) { // Vnode moved left patchVnode(oldEndVnode, newStartVnode, insertedVnodeQueue) 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) 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(parentElm, oldCh, oldStartIdx, oldEndIdx) } }
Several situations and processing of a loop comparison (the following - all refer to index -) The comparison is the node node of the comparison. The abbreviation is not rigorous and the comparison uses the sameVnode function, which is not true. Congruent
Conditions for the entire loop not to end oldStartIdx <= oldEndIdx && newStartIdx <= newEndIdx
newStart在old中发现一样的那么将这个移动到oldStart前
没有发现一样的那么创建一个放到oldStart之前
循环结束后并没有完成
还有一段判断才算完
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(parentElm, oldCh, oldStartIdx, oldEndIdx) }相信看了本文案例你已经掌握了方法,更多精彩请关注php中文网其它相关文章!
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