Nuxt/packages/vue-app/template/index.js

import Vue from 'vue'
<% if (store) { %>import Vuex from 'vuex'<% } %>
<% if (features.meta) { %>import Meta from 'vue-meta'<% } %>
<% if (features.componentClientOnly) { %>import ClientOnly from 'vue-client-only'<% } %>
<% if (features.deprecations) { %>import NoSsr from 'vue-no-ssr'<% } %>
import { createRouter } from './router.js'
import NuxtChild from './components/nuxt-child.js'
import NuxtError from '<%= components.ErrorPage ? components.ErrorPage : "./components/nuxt-error.vue" %>'
import Nuxt from './components/nuxt.js'
import App from '<%= appPath %>'
import { setContext, getLocation, getRouteData, normalizeError } from './utils'
<% if (store) { %>import { createStore } from './store.js'<% } %>

/* Plugins */
<%= isTest ? '/* eslint-disable camelcase */' : '' %>
<% plugins.forEach((plugin) => { %>import <%= plugin.name %> from '<%= plugin.name %>' // Source: <%= relativeToBuild(plugin.src) %> (mode: '<%= plugin.mode %>')
<% }) %>
<%= isTest ? '/* eslint-enable camelcase */' : '' %>

<% if (features.componentClientOnly) { %>
// Component: <ClientOnly>
Vue.component(ClientOnly.name, ClientOnly)
<% } %>
<% if (features.deprecations) { %>
// TODO: Remove in Nuxt 3: <NoSsr>
Vue.component(NoSsr.name, {
  ...NoSsr,
  render (h, ctx) {
    if (process.client && !NoSsr._warned) {
      NoSsr._warned = true
      <%= isTest ? '// eslint-disable-next-line no-console' : '' %>
      console.warn('<no-ssr> has been deprecated and will be removed in Nuxt 3, please use <client-only> instead')
    }
    return NoSsr.render(h, ctx)
  }
})
<% } %>
// Component: <NuxtChild>
Vue.component(NuxtChild.name, NuxtChild)
<% if (features.componentAliases) { %>Vue.component('NChild', NuxtChild)<% } %>

// Component NuxtLink is imported in server.js or client.js

// Component: <Nuxt>
Vue.component(Nuxt.name, Nuxt)

Object.defineProperty(Vue.prototype, '<%= globals.nuxt %>', {
  get() {
    const globalNuxt = this.$root ? this.$root.$options.<%= globals.nuxt %> : null
    if (process.client && !globalNuxt && typeof window !== 'undefined') {
      return window.<%= globals.nuxt %>
    }
    return globalNuxt
  },
  configurable: true
})

<% if (features.meta) {
// vue-meta configuration
const vueMetaOptions = {
  ...nuxtOptions.vueMeta,
  keyName: 'head', // the component option name that vue-meta looks for meta info on.
  attribute: 'data-n-head', // the attribute name vue-meta adds to the tags it observes
  ssrAttribute: 'data-n-head-ssr', // the attribute name that lets vue-meta know that meta info has already been server-rendered
  tagIDKeyName: 'hid' // the property name that vue-meta uses to determine whether to overwrite or append a tag
}
%>
Vue.use(Meta, <%= JSON.stringify(vueMetaOptions) %>)<%= isTest ? '// eslint-disable-line' : '' %>
<% } %>

<% if (features.transitions) { %>
const defaultTransition = <%=
  serialize(pageTransition)
  .replace('beforeEnter(', 'function(').replace('enter(', 'function(').replace('afterEnter(', 'function(')
  .replace('enterCancelled(', 'function(').replace('beforeLeave(', 'function(').replace('leave(', 'function(')
  .replace('afterLeave(', 'function(').replace('leaveCancelled(', 'function(').replace('beforeAppear(', 'function(')
  .replace('appear(', 'function(').replace('afterAppear(', 'function(').replace('appearCancelled(', 'function(')
%><%= isTest ? '// eslint-disable-line' : '' %>
<% } %>

<% if (store) { %>
const originalRegisterModule = Vuex.Store.prototype.registerModule

function registerModule (path, rawModule, options = {}) {
  const preserveState = process.client && (
    Array.isArray(path)
      ? !!path.reduce((namespacedState, path) => namespacedState && namespacedState[path], this.state)
      : path in this.state
  )
  return originalRegisterModule.call(this, path, rawModule, { preserveState, ...options })
}
<% } %>

async function createApp(ssrContext, config = {}) {
  const store = <%= store ? 'createStore(ssrContext)' : 'null' %>
  const router = await createRouter(ssrContext, config, { store })

  <% if (store) { %>
  // Add this.$router into store actions/mutations
  store.$router = router
    <% if (mode === 'universal') { %>
  // Fix SSR caveat https://github.com/nuxt/nuxt.js/issues/3757#issuecomment-414689141
  store.registerModule = registerModule
    <% } %>
  <% } %>

  // Create Root instance

  // here we inject the router and store to all child components,
  // making them available everywhere as `this.$router` and `this.$store`.
  const app = {
    <% if (features.meta) { %>
    <%= isTest ? '/* eslint-disable array-bracket-spacing, quotes, quote-props, semi, indent, comma-spacing, key-spacing, object-curly-spacing, space-before-function-paren, object-shorthand  */' : '' %>
    head: <%= serializeFunction(head) %>,
    <%= isTest ? '/* eslint-enable array-bracket-spacing, quotes, quote-props, semi, indent, comma-spacing, key-spacing, object-curly-spacing, space-before-function-paren, object-shorthand */' : '' %>
    <% } %>
    <% if (store) { %>store,<%  } %>
    router,
    nuxt: {
      <% if (features.transitions) { %>
      defaultTransition,
      transitions: [defaultTransition],
      setTransitions (transitions) {
        if (!Array.isArray(transitions)) {
          transitions = [transitions]
        }
        transitions = transitions.map((transition) => {
          if (!transition) {
            transition = defaultTransition
          } else if (typeof transition === 'string') {
            transition = Object.assign({}, defaultTransition, { name: transition })
          } else {
            transition = Object.assign({}, defaultTransition, transition)
          }
          return transition
        })
        this.$options.nuxt.transitions = transitions
        return transitions
      },
      <% } %>
      err: null,
      errPageReady: false,
      dateErr: null,
      error (err) {
        err = err || null
        app.context._errored = Boolean(err)
        err = err ? normalizeError(err) : null
        let nuxt = app.nuxt // to work with @vue/composition-api, see https://github.com/nuxt/nuxt.js/issues/6517#issuecomment-573280207
        if (this) {
          nuxt = this.nuxt || this.$options.nuxt
        }
        nuxt.dateErr = Date.now()
        nuxt.err = err
        nuxt.errPageReady = false
        // Used in src/server.js
        if (ssrContext) {
          ssrContext.nuxt.error = err
        }
        return err
      }
    },
    ...App
  }
  <% if (store) { %>
  // Make app available into store via this.app
  store.app = app
  <% } %>
  const next = ssrContext ? ssrContext.next : location => app.router.push(location)
  // Resolve route
  let route
  if (ssrContext) {
    route = router.resolve(ssrContext.url).route
  } else {
    const path = getLocation(router.options.base, router.options.mode)
    route = router.resolve(path).route
  }

  // Set context to app.context
  await setContext(app, {
    <% if (store) { %>store,<% } %>
    route,
    next,
    error: app.nuxt.error.bind(app),
    payload: ssrContext ? ssrContext.payload : undefined,
    req: ssrContext ? ssrContext.req : undefined,
    res: ssrContext ? ssrContext.res : undefined,
    beforeRenderFns: ssrContext ? ssrContext.beforeRenderFns : undefined,
    beforeSerializeFns: ssrContext ? ssrContext.beforeSerializeFns : undefined,
    ssrContext
  })

  function inject(key, value) {
    if (!key) {
      throw new Error('inject(key, value) has no key provided')
    }
    if (value === undefined) {
      throw new Error(`inject('${key}', value) has no value provided`)
    }

    key = '$' + key
    // Add into app
    app[key] = value
    // Add into context
    if (!app.context[key]) {
      app.context[key] = value
    }
    <% if (store) { %>
    // Add into store
    store[key] = app[key]
    <% } %>
    // Check if plugin not already installed
    const installKey = '__<%= globals.pluginPrefix %>_' + key + '_installed__'
    if (Vue[installKey]) {
      return
    }
    Vue[installKey] = true
    // Call Vue.use() to install the plugin into vm
    Vue.use(() => {
      if (!Object.prototype.hasOwnProperty.call(Vue.prototype, key)) {
        Object.defineProperty(Vue.prototype, key, {
          get () {
            return this.$root.$options[key]
          }
        })
      }
    })
  }

  // Inject runtime config as $config
  inject('config', config)

  <% if (store) { %>
  if (process.client) {
    // Replace store state before plugins execution
    if (window.<%= globals.context %> && window.<%= globals.context %>.state) {
      store.replaceState(window.<%= globals.context %>.state)
    }
  }
  <% } %>

  // Add enablePreview(previewData = {}) in context for plugins
  if (process.static && process.client) {
    app.context.enablePreview = function (previewData = {}) {
      app.previewData = Object.assign({}, previewData)
      inject('preview', previewData)
    }
  }
  // Plugin execution
  <%= isTest ? '/* eslint-disable camelcase */' : '' %>
  <% plugins.forEach((plugin) => { %>
  <% if (plugin.mode == 'client') { %>
  if (process.client && typeof <%= plugin.name %> === 'function') {
    await <%= plugin.name %>(app.context, inject)
  }
  <% } else if (plugin.mode == 'server') { %>
  if (process.server && typeof <%= plugin.name %> === 'function') {
    await <%= plugin.name %>(app.context, inject)
  }
  <% } else { %>
  if (typeof <%= plugin.name %> === 'function') {
    await <%= plugin.name %>(app.context, inject)
  }
  <% } %>
  <% }) %>
  <%= isTest ? '/* eslint-enable camelcase */' : '' %>
  // Lock enablePreview in context
  if (process.static && process.client) {
    app.context.enablePreview = function () {
      console.warn('You cannot call enablePreview() outside a plugin.')
    }
  }

  // Wait for async component to be resolved first
  await new Promise((resolve, reject) => {
    // Ignore 404s rather than blindly replacing URL in browser
    if (process.client) {
      const { route } = router.resolve(app.context.route.fullPath)
      if (!route.matched.length) {
        return resolve()
      }
    }
    router.replace(app.context.route.fullPath, resolve, (err) => {
      // https://github.com/vuejs/vue-router/blob/v3.4.3/src/util/errors.js
      if (!err._isRouter) return reject(err)
      if (err.type !== 2 /* NavigationFailureType.redirected */) return resolve()

      // navigated to a different route in router guard
      const unregister = router.afterEach(async (to, from) => {
        if (process.server && ssrContext && ssrContext.url) {
          ssrContext.url = to.fullPath
        }
        app.context.route = await getRouteData(to)
        app.context.params = to.params || {}
        app.context.query = to.query || {}
        unregister()
        resolve()
      })
    })
  })

  return {
    <% if(store) { %>store,<%  } %>
    app,
    router
  }
}

export { createApp, NuxtError }