选中第一个，什么添加不了，其它都可以？
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>ADD添加实例</title>
<script type="text/javascript" src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
<style>
.active{ background: green }
/*ul li{ list-style: none; }*/
</style>
</head>
<body>
<div id="app">
<ul>
<li v-for="(item,index) in lists"
@click="choose(index)"
:class="{active: index==current && current !== '' }"
:key="index"
>
{{ item }}
</li>
</ul>
<button type="button" @click="add()">添加</button>
<ul>
<li v-for="(item,index) in target" :key="index">
{{ item }}
</li>
</ul>
</div>
<script>
const vm=new Vue({
el:'#app',
data:{
current:"",
lists:[1,2,3,4,5,6,7,8,9],
target:[]
},
methods:{
choose(index){
console.log(index);
this.current=index;
},
add(){
if(this.current==""){ return }
this.target.push(this.lists[this.current]);
this.current="";
}
}
})
</script>
</body>
</html>
