types/nuxt.d.ts

import Vue from 'vue'
import { Store } from 'vuex'

// ComponentOptions is declared in types/options.d.ts
declare module 'vue/types/options' {

  interface NuxtContext<V extends Vue> {
    app: V,
    isClient: boolean,
    isServer: boolean,
    isStatic: boolean,
    isDev: boolean,
    store: Store<any>, // Consider vuex-typex in future
    env: object,
    params: object,
    query: object
  }

  interface ComponentOptions<V extends Vue> {
    asyncData?(context: NuxtContext<V>): Promise<object> | object
    fetch?(context: NuxtContext<V>): Promise<object> | object
  }
}