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 liuqimichale
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/* @flow */
import { makeMap, isBuiltInTag, cached, no } from 'shared/util'
let isStaticKey
let isPlatformReservedTag
const genStaticKeysCached = cached(genStaticKeys)
/**
* Goal of the optimizer: walk the generated template AST tree
* and detect sub-trees that are purely static, i.e. parts of
* the DOM that never needs to change.
*
* Once we detect these sub-trees, we can:
*
* 1. Hoist them into constants, so that we no longer need to
* create fresh nodes for them on each re-render;
* 2. Completely skip them in the patching process.
*/
export function optimize (root: ?ASTElement, options: CompilerOptions) {
if (!root) return
isStaticKey = genStaticKeysCached(options.staticKeys || '')
isPlatformReservedTag = options.isReservedTag || no
// first pass: mark all non-static nodes.
markStatic(root)
// second pass: mark static roots.
markStaticRoots(root, false)
}
function genStaticKeys (keys: string): Function {
return makeMap(
'type,tag,attrsList,attrsMap,plain,parent,children,attrs' +
(keys ? ',' + keys : '')
)
}
function markStatic (node: ASTNode) {
node.static = isStatic(node)
if (node.type === 1) {
// do not make component slot content static. this avoids
// 1. components not able to mutate slot nodes
// 2. static slot content fails for hot-reloading
if (
!isPlatformReservedTag(node.tag) &&
node.tag !== 'slot' &&
node.attrsMap['inline-template'] == null
) {
return
}
for (let i = 0, l = node.children.length; i < l; i++) {
const child = node.children[i]
markStatic(child)
if (!child.static) {
node.static = false
}
}
if (node.ifConditions) {
for (let i = 1, l = node.ifConditions.length; i < l; i++) {
const block = node.ifConditions[i].block
markStatic(block)
if (!block.static) {
node.static = false
}
}
}
}
}
function markStaticRoots (node: ASTNode, isInFor: boolean) {
if (node.type === 1) {
if (node.static || node.once) {
node.staticInFor = isInFor
}
// For a node to qualify as a static root, it should have children that
// are not just static text. Otherwise the cost of hoisting out will
// outweigh the benefits and it's better off to just always render it fresh.
if (node.static && node.children.length && !(
node.children.length === 1 &&
node.children[0].type === 3
)) {
node.staticRoot = true
return
} else {
node.staticRoot = false
}
if (node.children) {
for (let i = 0, l = node.children.length; i < l; i++) {
markStaticRoots(node.children[i], isInFor || !!node.for)
}
}
if (node.ifConditions) {
for (let i = 1, l = node.ifConditions.length; i < l; i++) {
markStaticRoots(node.ifConditions[i].block, isInFor)
}
}
}
}
function isStatic (node: ASTNode): boolean {
if (node.type === 2) { // expression
return false
}
if (node.type === 3) { // text
return true
}
return !!(node.pre || (
!node.hasBindings && // no dynamic bindings
!node.if && !node.for && // not v-if or v-for or v-else
!isBuiltInTag(node.tag) && // not a built-in
isPlatformReservedTag(node.tag) && // not a component
!isDirectChildOfTemplateFor(node) &&
Object.keys(node).every(isStaticKey)
))
}
function isDirectChildOfTemplateFor (node: ASTElement): boolean {
while (node.parent) {
node = node.parent
if (node.tag !== 'template') {
return false
}
if (node.for) {
return true
}
}
return false
}
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