SOURCE

new Vue({
  el:"#app",
  data:{
    borderRadius:'0%',
    isRed:true
  },
  methods:{
    start:function(){
      var vm=this
      setInterval(function(){
        vm.isRed=!vm.isRed;
      },1000)
    },
    changeStyle:function(){
      if(this.borderRadius=='50%'){
        this.borderRadius='0%'
      }else{
        this.borderRadius='50%'
      }
    }
  }
})

<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
<div id="app">
  <div class="main" @click='changeStyle' :style="{'border-radius':borderRadius}"></div>
  <button @click="start">开始</button>
  <div class="main" :class="{red:isRed,blue:!isRed}"></div>
</div>

.main{height:150px;width:150px;background-color:gray}
.red{background-color:red}
.blue{background-color:blue}