javascript - 怎么在vue单文件组件里获取router

<template>
    <p>
        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>
    </p>
</template>
<script>

    export default{
        methods:{
            gta1(){
                router.push({path:'a'}) //这里报错了， “router is not defined”
            }
        }
    }
</script>

求问，怎么才能获取到router，实现编程式导航？