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>
 </div>
</template>
<script>
import Store from './store'
export default {
 name: 'app',
 data () {
 return {
  title: 'this is a todo list',
  items:Store.fetch(),
  newItem:''
 }
 },
 watch:{
  items:{
  handler(items){  //經過變化的數組會作為第一個參數傳入
   Store.save(items)
   console.log(Store.fetch());
  },
  deep:true  //深度復制
  }
 },
 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>