详解为什么Vue中的v-if和v-for不建议一起用

<Modal v-if="isShow" />
 
<li v-for="item in items" :key="item.id">
  {{ item.label }}
</li>

<div id="app">
  <p v-if="isShow" v-for="item in items">
    {{ item.title }}
  </p>
</div>

const app = new Vue({
 el: "#app",
 data() {
  return {
   items: [
    { title: "foo" },
    { title: "baz" }]
  }
 },
 computed: {
  isShow() {
   return this.items && this.items.length > 0
  }
 }
})

ƒ anonymous() {
 with (this) { return 
  _c('div', { attrs: { "id": "app" } }, 
  _l((items), function (item) 
  { return (isShow) ? _c('p', [_v("\n" + _s(item.title) + "\n")]) : _e() }), 0) }
}

<div id="app">
  <template v-if="isShow">
    <p v-for="item in items">{{item.title}}</p>
  </template>
</div>

ƒ anonymous() {
 with(this){return 
  _c('div',{attrs:{"id":"app"}},
  [(isShow)?[_v("\n"),
  _l((items),function(item){return _c('p',[_v(_s(item.title))])})]:_e()],2)}
}

export function genElement (el: ASTElement, state: CodegenState): string {
 if (el.parent) {
  el.pre = el.pre || el.parent.pre
 }
 if (el.staticRoot && !el.staticProcessed) {
  return genStatic(el, state)
 } else if (el.once && !el.onceProcessed) {
  return genOnce(el, state)
 } else if (el.for && !el.forProcessed) {
  return genFor(el, state)
 } else if (el.if && !el.ifProcessed) {
  return genIf(el, state)
 } else if (el.tag === 'template' && !el.slotTarget && !state.pre) {
  return genChildren(el, state) || 'void 0'
 } else if (el.tag === 'slot') {
  return genSlot(el, state)
 } else {
  // component or element
  ...
}

<template v-if="isShow">
  <p v-for="item in items">
</template>

computed: {
  items: function() {
   return this.list.filter(function (item) {
    return item.isShow
   })
  }
}