SOURCE

function add(){
            console.log("我已经执行了");
        //    app.arr[1]='ddd';
           Vue.set(app.arr,1,'ddd');
        }
        var outData={
            arr:['aaa','bbb','ccc']
        };
        var app=new Vue({
            el:'#app',
            data:outData
        })

 <div id="app">
        <ul>
            <li v-for=" aa in arr">{{aa}}</li>
        </ul>

    </div>
    <button onclick="add()">外部添加</button>