How to pass parameters from parent to child component in vue.js

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=&#39;toogleFinish(item)&#39;>
    {{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=&#39;you die!&#39;></Component-a>
 </div>
</template>
<script>
import Store from &#39;./store&#39;
import ComponentA from &#39;./components/componentA&#39;  //该组件会被加载到该页面
export default {
 name: &#39;app&#39;,
 data () {
  return {
   title: &#39;this is a todo list&#39;,
   items:Store.fetch(),
   newItem:&#39;&#39;
  }
 },
 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 = &#39;&#39;
  }
 }
}
</script>
<style>
#app {
 font-family: &#39;Avenir&#39;, 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:&#39;Hello form component a&#39;
   }
 },
 props:[&#39;msgfromfather&#39;],//自组件接收数据
 methods:{
   onClickMe(){
     console.log(this.msgfromfather);
   }
 }
}
</script>
<style scoped>
</style>