Snabbdom 源码 diff 算法解说
https://github.com/Snabbdom/Snabbdom 上的一个例子代码
- vdom 核心概念：h、vnode、patch、diff、key等
- vdom 存在的价值：数据驱动视图，控制 DOM 操作
import { init } from 'snabbdom/init'
import { classModule } from 'snabbdom/modules/class'
import { propsModule } from 'snabbdom/modules/props'
import { styleModule } from 'snabbdom/modules/style'
import { eventListenersModule } from 'snabbdom/modules/eventlisteners'
import { h } from 'snabbdom/h' // helper function for creating vnodes
var patch = init([ // Init patch function with chosen modules
classModule, // makes it easy to toggle classes
propsModule, // for setting properties on DOM elements
styleModule, // handles styling on elements with support for animations
eventListenersModule, // attaches event listeners
])
var container = document.getElementById('container')
var vnode = h('div#container.two.classes', { on: { click: someFn } }, [
h('span', { style: { fontWeight: 'bold' } }, 'This is bold'),
' and this is just normal text',
h('a', { props: { href: '/foo' } }, 'I'll take you places!')
])
// Patch into empty DOM element – this modifies the DOM as a side effect
patch(container, vnode)
var newVnode = h('div#container.two.classes', { on: { click: anotherEventHandler } }, [
h('span', { style: { fontWeight: 'normal', fontStyle: 'italic' } }, 'This is now italic type'),
' and this is still just normal text',
h('a', { props: { href: '/bar' } }, 'I'll take you places!')
])
// Second `patch` invocation
patch(vnode, newVnode) // Snabbdom efficiently updates the old view to the new state
根据上面的例子，一起先看下文件 h.ts 中的 h 函数
export function h (sel: any, b?: any, c?: any): VNode {
...
// 返回 vnode
return vnode(sel, data, children, text, undefined);
};
接着是 snabbdom.ts 文件中的 patch 函数
return function patch (oldVnode: VNode | Element, vnode: VNode): VNode {
let i: number, elm: Node, parent: Node;
const insertedVnodeQueue: VNodeQueue = [];
// 执行 pre hook
for (i = 0; i < cbs.pre.length; ++i) cbs.pre[i]();
// 第一个参数不是 vnode
if (!isVnode(oldVnode)) {
// 创建一个空的 vnode ，关联到这个 DOM 元素
oldVnode = emptyNodeAt(oldVnode);
}
// 相同的 vnode（key 和 sel 都相等）
if (sameVnode(oldVnode, vnode)) {
// vnode 对比
patchVnode(oldVnode, vnode, insertedVnodeQueue);
// 不同的 vnode ，直接删掉重建
} else {
elm = oldVnode.elm!;
parent = api.parentNode(elm);
// 重建
createElm(vnode, insertedVnodeQueue);
if (parent !== null) {
api.insertBefore(parent, vnode.elm!, api.nextSibling(elm));
removeVnodes(parent, [oldVnode], 0, 0);
}
}
for (i = 0; i < insertedVnodeQueue.length; ++i) {
insertedVnodeQueue[i].data!.hook!.insert!(insertedVnodeQueue[i]);
}
for (i = 0; i < cbs.post.length; ++i) cbs.post[i]();
return vnode;
};
注意上面的 sameVnode 函数
function sameVnode (vnode1: VNode, vnode2: VNode): boolean {
// key 和 sel 都相等
// undefined === undefined // true
return vnode1.key === vnode2.key && vnode1.sel === vnode2.sel;
}
然后就是对比的 patchVnode 函数
function patchVnode (oldVnode: VNode, vnode: VNode, insertedVnodeQueue: VNodeQueue) {
// 执行 prepatch hook
const hook = vnode.data?.hook;
hook?.prepatch?.(oldVnode, vnode);
// 设置 vnode.elem
const elm = vnode.elm = oldVnode.elm!;
// 旧 children
let oldCh = oldVnode.children as VNode[];
// 新 children
let ch = vnode.children as VNode[];
if (oldVnode === vnode) return;
// hook 相关
if (vnode.data !== undefined) {
for (let i = 0; i < cbs.update.length; ++i) cbs.update[i](oldVnode, vnode);
vnode.data.hook?.update?.(oldVnode, vnode);
}
// vnode.text === undefined （vnode.children 一般有值）
if (isUndef(vnode.text)) {
// 新旧都有 children
if (isDef(oldCh) && isDef(ch)) {
if (oldCh !== ch) updateChildren(elm, oldCh, ch, insertedVnodeQueue);
// 新 children 有，旧 children 无 （旧 text 有）
} else if (isDef(ch)) {
// 清空 text
if (isDef(oldVnode.text)) api.setTextContent(elm, '');
// 添加 children
addVnodes(elm, null, ch, 0, ch.length - 1, insertedVnodeQueue);
// 旧 child 有，新 child 无
} else if (isDef(oldCh)) {
// 移除 children
removeVnodes(elm, oldCh, 0, oldCh.length - 1);
// 旧 text 有
} else if (isDef(oldVnode.text)) {
api.setTextContent(elm, '');
}
// else : vnode.text !== undefined （vnode.children 无值）
} else if (oldVnode.text !== vnode.text) {
// 移除旧 children
if (isDef(oldCh)) {
removeVnodes(elm, oldCh, 0, oldCh.length - 1);
}
// 设置新 text
api.setTextContent(elm, vnode.text!);
}
hook?.postpatch?.(oldVnode, vnode);
}
最后看下比较关键的 updateChildren 函数
function updateChildren (parentElm: Node,
oldCh: VNode[],
newCh: VNode[],
insertedVnodeQueue: VNodeQueue) {
let oldStartIdx = 0, 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: KeyToIndexMap | undefined;
let idxInOld: number;
let elmToMove: VNode;
let before: any;
while (oldStartIdx <= oldEndIdx && newStartIdx <= newEndIdx) {
if (oldStartVnode == null) {
oldStartVnode = oldCh[++oldStartIdx]; // Vnode might have been moved left
} else if (oldEndVnode == null) {
oldEndVnode = oldCh[--oldEndIdx];
} else if (newStartVnode == null) {
newStartVnode = newCh[++newStartIdx];
} else if (newEndVnode == null) {
newEndVnode = newCh[--newEndIdx];
// 开始和开始对比
} else if (sameVnode(oldStartVnode, newStartVnode)) {
patchVnode(oldStartVnode, newStartVnode, insertedVnodeQueue);
oldStartVnode = oldCh[++oldStartIdx];
newStartVnode = newCh[++newStartIdx];
// 结束和结束对比
} else if (sameVnode(oldEndVnode, newEndVnode)) {
patchVnode(oldEndVnode, newEndVnode, insertedVnodeQueue);
oldEndVnode = oldCh[--oldEndIdx];
newEndVnode = newCh[--newEndIdx];
// 开始和结束对比
} else if (sameVnode(oldStartVnode, newEndVnode)) { // Vnode moved right
patchVnode(oldStartVnode, newEndVnode, insertedVnodeQueue);
api.insertBefore(parentElm, oldStartVnode.elm!, api.nextSibling(oldEndVnode.elm!));
oldStartVnode = oldCh[++oldStartIdx];
newEndVnode = newCh[--newEndIdx];
// 结束和开始对比
} else if (sameVnode(oldEndVnode, newStartVnode)) { // Vnode moved left
patchVnode(oldEndVnode, newStartVnode, insertedVnodeQueue);
api.insertBefore(parentElm, oldEndVnode.elm!, oldStartVnode.elm!);
oldEndVnode = oldCh[--oldEndIdx];
newStartVnode = newCh[++newStartIdx];
// 以上四个都未命中
} else {
if (oldKeyToIdx === undefined) {
oldKeyToIdx = createKeyToOldIdx(oldCh, oldStartIdx, oldEndIdx);
}
// 拿新节点 key ，能否对应上 oldCh 中的某个节点的 key
idxInOld = oldKeyToIdx[newStartVnode.key as string];
// 没对应上
if (isUndef(idxInOld)) { // New element
api.insertBefore(parentElm, createElm(newStartVnode, insertedVnodeQueue), oldStartVnode.elm!);
newStartVnode = newCh[++newStartIdx];
// 对应上了
} else {
// 对应上 key 的节点
elmToMove = oldCh[idxInOld];
// sel 是否相等（sameVnode 的条件）
if (elmToMove.sel !== newStartVnode.sel) {
// New element
api.insertBefore(parentElm, createElm(newStartVnode, insertedVnodeQueue), oldStartVnode.elm!);
// sel 相等，key 相等
} else {
patchVnode(elmToMove, newStartVnode, insertedVnodeQueue);
oldCh[idxInOld] = undefined as any;
api.insertBefore(parentElm, elmToMove.elm!, oldStartVnode.elm!);
}
newStartVnode = newCh[++newStartIdx];
}
}
}
if (oldStartIdx <= oldEndIdx || newStartIdx <= newEndIdx) {
if (oldStartIdx > oldEndIdx) {
before = newCh[newEndIdx + 1] == null ? null : newCh[newEndIdx + 1].elm;
addVnodes(parentElm, before, newCh, newStartIdx, newEndIdx, insertedVnodeQueue);
} else {
removeVnodes(parentElm, oldCh, oldStartIdx, oldEndIdx);
}
}
}
