Vue.js 如何在 vue 组件之外访问$apollo

如何让apollo在vue组件外部可访问.

我正在验证用户是否存在，然后允许路由继续.

{
        path: '/:username',
        name: 'userProfilePage',
        component: userProfilePage,
        beforeEnter(routeTo, routeFrom, next) {
            userExist(routeTo.params.username)
            next()
        }

将username作为参数传递给userExist函数.

import gql from "graphql-tag"

export default function userExist(username) {
    this.$apollo
        .query({
            query: gql`
        query($username: String!) {
            login(username: $username) {
                username
                email
            }
        }
    `,
            variables: {
                username: username
            }
        })
        .then(res => {
            console.log(res);
            return res
        })
        .catch(err => {
            console.log(err);
            return err
        });
}

但它正在输出错误:

阿波罗客户端代码

import Vue from 'vue'
import App from './App.vue'
import VueApollo from 'vue-apollo';
import { ApolloClient } from 'apollo-client'
import { HttpLink } from 'apollo-link-http'
import { InMemoryCache } from 'apollo-cache-inmemory'
import router from './routes.js'

Vue.config.productionTip = false

const httpLink = new HttpLink({
    uri: process.env.VUE_APP_DB_URL,
})

const cache = new InMemoryCache()

const apolloClient = new ApolloClient({
    link: httpLink,
    cache
})

Vue.use(VueApollo)

const apolloProvider = new VueApollo({
    defaultClient: apolloClient,
})

new Vue({
    render: h => h(App),
    router,
    apolloProvider
}).$mount('#app')