<template>    <div>        a.vue        <router-link to="/a/a1">a1</router-link>        <router-link to="/a/a2">a2</router-link>        <br>        <button @click="gta1()">a1</button>        <router-view></router-view>    </div></template><script>    export default{        methods:{            gta1(){                router.push({path:'a'}) //這里報錯了， “router is not defined”            }        }    }</script>求問，怎么才能獲取到router，實現編程式導航？