灵活运用Vue指令：探究v-if和v-for的使用技巧和注意事项

<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
      })
    }
}