How to access '$apollo' outside vue component?

Question

How to make apollo accessible outside vue component.

I am verifying if the user exist and then allow the route to proceed further.

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

Passing the username as a parameter to the userExist function.

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
        });
}

But it is outputting the error:

Apollo client code

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')

Answer 1

So instead of initializing the apollo client in the App.vue file, initialize it in another file. Something like clients.js, and export that client:

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

const cache = new InMemoryCache()

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

Once done, import that in App.vue file like this:

import { apolloClient } from './clients.js';

Vue.use(VueApollo)

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

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

Once done, import that client in any other file you want:

import { apolloClient } from './client.js';
import gql from "graphql-tag"

export default function userExist(username) {
apolloClient
    .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
    });
}