vue.js里如何做到父向子组件传参

const STORAGE_KEY = 'todos-vue.js'
export default{
 fetch(){
 return JSON.parse(window.localStorage.getItem(STORAGE_KEY) || '[]')
 },
 save(items){
 window.localStorage.setItem(STORAGE_KEY,JSON.stringify(items));
 }
}

<template>
 <div id="app">
 <h1 v-text="title"></h1>
 <input v-model="newItem" v-on:keyup.enter="addNew"/>
 <ul>
 <li v-for="item in items" v-bind:class="{finished:item.isFinished}" v-on:click='toogleFinish(item)'>
 {{item.label}}
 </li>
 </ul>
 <!-- 使用组件，注意驼峰命名法转化成短线 -->
 <!-- 向自组件传数据 -->
 <Component-a msgfromfather='you die!'></Component-a>
 </div>
</template>
<script>
import Store from './store'
import ComponentA from './components/componentA' //该组件会被加载到该页面
export default {
 name: 'app',
 data () {
 return {
 title: 'this is a todo list',
 items:Store.fetch(),
 newItem:''
 }
 },
 components:{ //注册组件
 ComponentA
 },
 watch:{
 items:{
 handler(items){ //经过变化的数组会作为第一个参数传入
 Store.save(items)
 },
 deep:true //深度复制
 }
 },
 methods:{
 toogleFinish(item){
 item.isFinished = !item.isFinished
 },
 addNew(){
 this.items.push({
 label:this.newItem,
 isFinished:false,
 })
 this.newItem = ''
 }
 }
}
</script>
<style>
#app {
 font-family: 'Avenir', Helvetica, Arial, sans-serif;
 -webkit-font-smoothing: antialiased;
 -moz-osx-font-smoothing: grayscale;
 text-align: center;
 color: #2c3e50;
 margin-top: 60px;
}
.finished{
 text-decoration: underline;
}
</style>

<template>
 <div class="hello">
 <h1>{{msg}}</h1>
 <h2>{{msgfromfather}}</h2>
 <button v-on:click="onClickMe">Click!</button>
 </div>
</template>
<<script>
export default {
 data(){
 return{
 msg:'Hello form component a'
 }
 },
 props:['msgfromfather'],//自组件接收数据
 methods:{
 onClickMe(){
 console.log(this.msgfromfather);
 }
 }
}
</script>
<style scoped>
</style>