主要解决了在v-for时，如何给每个item添加动态的样式，即是说，鼠标滑动到某一项时，可以单独改变某一项的样式，同时添加按钮等操作。以及删除某一项的操作。

<template>
  <div class="hello">
      <ul>
          <li   v-for="(item, itemIndex) in test" 
                :key="item.id" 
                :class="{defaultClass: itemIndex === isActive}"
                @mouseenter="onMouseEnter(itemIndex)" 
                @mouseleave="onMouseLeave">
              {{ itemIndex+1 }} :{{ item.title }}
              <button v-if="isActive === itemIndex" @click="deleteItem(itemIndex)">删除({{itemIndex+1}})</button>
          </li>
      </ul>
  </div>
</template>

<script>
export default {
  name: 'HelloWorld',
  data () {
    return {
      test: [
          {     
              id: 1,
              title: 'title first'
          },
          {
              id: 2,
              title: 'title second'
          },
          {
              id: 3,
              title: 'title third'
          }
      ],
      isActive: ''
    }
  },
  methods: {
      onMouseEnter(index) {
          this.isActive = index
      },
      onMouseLeave() {
          this.isActive = ''
      },
      deleteItem(index) {
          this.test.splice(index, 1)
      }
  },
  computed: {
      
  }
}
</script>

<!-- Add "scoped" attribute to limit CSS to this component only -->
<style scoped>
h1, h2 {
  font-weight: normal;
}
ul {
  list-style-type: none;
  padding: 0;
}
li {
  /* display: inline-block; */
  margin:10px;
}
a {
  color: #42b983;
}
.defaultClass{
    background-color: red;
}
</style>