<style>
    li{list-style:none;display: inline-block;padding:10px;}
    .gradient{background:grey;}
    .active{background:red;}

    </style>
    <script src="vue.js"></script>

    
    <script>
        window.onload = function(){
            var menuBar = new Vue({
    el:'#menu',
    data:{
        choices:[
            {selected:'搜店'},
            {selected:'地址'},
            {selected:'优惠券'},
            {selected:'全文'},
            {selected:'视频'}
        ],
        activeMenu:''
    },
    methods:{
        activeBar:function(item){
        
        this.activeMenu = item
    }
}
});

        }
    </script>

<ul class="menu" id="menu">
             <li class="gradient" v-for="item in choices" v-on:click="activeBar(item)" :class="{active: activeMenu == item}" >{{item.selected}}</li> 

我想初始化第一個li是active，是用v-if判斷嗎還是？