vue3中的defineProps，watch，computed

在vue3的setup语法糖中，defineProps不需要引入了

<script setup>
import { computed } from '@vue/reactivity';
import { onMounted, watch } from 'vue';
let props = defineProps(['playlist'])
console.log(props.playlist) // 不能获取值，因为父组件这时候还没传值过来
// onMounted(() => {
//     setTimeout(() => {
//         console.log('23:', props.playlist); // ok
//     }, 800)
// })
let bmsg = watch(() => props.playlist, (a, pre) => { // watch函数监听props.playlist的值
    console.log("2345：", a);
    console.log("2345pre：", pre);
},{immediate:true}) // immediate:true，让watch立即执行回调打印值
let msg = computed(() => { // 立即执行
    console.log('23:', props.playlist);
    return props.playlist
})