vue3.0——组件通信props、emit

//子组件
<template>
  <div class="hello">
    <span>{
   
   { msg }}</span>
    <div></div>
    <span>{
   
   { num }}</span>
    <button @click="add">+</button>
  </div>
</template>

<script>
import {
     
      ref, watch } from "vue";
export default {
     
     
  name: "HelloWorld",
  props: {
     
     
    msg: {
     
     
      type: String,
      default: () => "默认值",
    },
  },
  setup(props,context) {
     
     
    //     vue3.0           vue2.0
    // context.attrs === this.$attrs
    // context.slots === this.$slots
    // context.emit  === this.$emit
    const num = ref(0);
    const obj = ref("这是儿子的信息哦！")
    watch(
      () => props.msg,
      (count, prevCount) => {
     
     
        console.log(count);
        console.log(prevCount);
      }
    );
    function add() {
     
     
    num.value += 1;
    context.emit("sonMsg",obj.value);
    }
    return {
     
     
      num,
      add,
    };
  },
};
</script>
<style scoped lang="less">
</style>

//父级
<template>
  <div id="home">
    <div>{
   
   { msg }}</div>
    <button @click="change">改变</button>
    <input type="checkbox" />
    <HelloWorld :msg = msg @sonMsg="farthMsg"></HelloWorld>
  </div>
</template>

<script>
import {
     
     
  ref, //ref() 函数用来根据给定的值创建一个(响应式的数据对象)，传入的为基本数据类型，例如字符串、数字、boolean 等,返回值是一个对象，这个对象上只包含一个 value 属性

} from "vue";
import HelloWorld from "@/components/HelloWorld.vue";
export default {
     
     
  name: "Home",
  components:{
     
     
  HelloWorld
  },
  setup() {
     
     
    const msg = ref("这是父组件信息哦！");
    function change(){
     
     
      msg.value = "这是父亲的信息哦！";
    }
    function farthMsg(res){
     
     
      console.log(res)
        msg.value = res;
    }
    return {
     
     
     msg,
     change,
     farthMsg
    };
  },
};
</script>