vue-$nextTick个人理解

vue学习笔记

$nextTick

<template>
  <div class="home">
    <span ref="title">{{name}}</span>
    <img alt="Vue logo" src="../assets/logo.png" />
    <HelloWorld msg="Welcome to Your Vue.js App" />
  </div>
</template>

<script>
// @ is an alias to /src
import HelloWorld from "@/components/HelloWorld.vue";

export default {
  name: "Home",
  data(){
    return{
      name:'小红'
    }
  },
  components: {
    HelloWorld
  },
  async mounted() {
    this.name='小米'
    console.log(3,this.$refs.title);
    await this.$nextTick()
    console.log(4,this.$refs.title);
  },
  async created() {
    this.name='小猫'
    console.log(1,this.$refs.title);
    await this.$nextTick()
    console.log(2,this.$refs.title);
  }
};
</script>

<template>
  <div class="home">
    <span ref="title">{{name}}</span>
    <img alt="Vue logo" src="../assets/logo.png" />
    <HelloWorld msg="Welcome to Your Vue.js App" />
  </div>
</template>

<script>
// @ is an alias to /src
import HelloWorld from "@/components/HelloWorld.vue";

export default {
  name: "Home",
  data(){
    return{
      name:'小红'
    }
  },
  components: {
    HelloWorld
  },
  async mounted() {
    // this.name='小米'
    // console.log(3,this.$refs.title);
    // await this.$nextTick()
    // console.log(4,this.$refs.title);
    console.log(1);
    await console.log(2)
    console.log(3)

  },
  async created() {
    console.log(4);
    await console.log(5)
    console.log(6)
    // this.name='小猫'
    // console.log(1,this.$refs.title);
    // await this.$nextTick()
    // console.log(2,this.$refs.title);
  }
};
</script>

实现原理

分为宏任务和微任务

• 微任务检测Promise不支持降级为宏任务
• 宏任务检测setImmediate不支持就检测MessageChannel，最后降级为setTimeout

将callback压入callbacks数组，在下一个tick时遍历callbacks数组 这里使用 callbacks 而不是直接在 nextTick 中执行回调函数的原因是保证在同一个 tick 内多次执行 nextTick，不会开启多个异步任务，而把这些异步任务都压成一个同步任务，在下一个 tick 执行完毕。