@nuxtjs/apollo用の VueApollo 型拡張宣言ファイル。

vue-apollo.d.ts

declare module 'vue-apollo/types/vue-apollo' {
  import { ApolloClient } from 'apollo-client'
  import {
    VueApolloOptions,
    WatchLoading,
    ErrorHandler
  } from 'vue-apollo/types/options'

  interface VueApollo {
    defaultClient: ApolloClient<{}>
    defaultOptions: VueApolloOptions<{}>
    clients: { [key: string]: ApolloClient<{}> }
    watchLoading: WatchLoading<{}>
    errorHandler: ErrorHandler<{}>
  }
}