bug code:
<li v-for="item in items" v-bind:class="{finished: item.isFinished}" v-on:click="toggleFinish(item)">
{{item.label}}
</li>
right code:
<li v-for="item in items" :key="item.label" v-bind:class="{finished: item.isFinished}" v-on:click="toggleFinish(item)">
{{item.label}}
</li>
增加:key=“item.label”