app.vue

<template>
  <div>
    <h1>App 根元件</h1>

    <hr />

    <!-- 使用元件 -->
    <my-home></my-home>
  </div>
</template>

<script>
// 匯入元件
import MyHome from './Home.vue'

export default {
  name: 'MyApp',
  // 註冊元件
  components: {
    MyHome,
  },
}
 
</script>

<style lang="less" scoped></style>

<template>
  <div class="home-container">
    <h3 v-color="'red'">MyHome 元件 --- {{ count }}</h3>
    <hr />

    <input type="text" class="form-control" v-focus v-color="'cyan'" />
    <button 
 
type="button" class="btn btn-primary" @click="count += 1">+1</button>
  </div>
</template>

<script>
export default {
  name: 'MyHome',
  data() {
    return {
      count: 0,
    }
  },
  directives: {
    // focus: {
    //   mounted(el) {
    //     el.focus()
    //   },
    // },
  },
}
 
</script>

<style lang="less" scoped>
.home-container {
  border: 1px solid #efefef;
  box-shadow: 0px 1px 10px #efefef;
  border-radius: 4px;
  padding: 20px;
  margin: 20px;
}

input.form-control {
  width: 280px;
}
</style>

 main.js（自定義全域性指令）

// 宣告全域性自定義指令
app.directive('focus', {
  mounted(el) {
    console.log('mounted')
    el.focus()
  },
  updated(el) {
    console.log('updated')
    el.focus()
  },
})