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

import Vue from 'vue'
import Vuex from 'vuex'

Vue.use(Vuex)

let storeData = {}

let files;

void function updateModules() {
  files = require.context('@/<%= dir.store %>', true, /^\.\/(?!<%= ignorePrefix %>)[^.]+\.(<%= extensions %>)$/)
  const filenames = files.keys()

  // Check if {dir.store}/index.js exists
  const indexFilename = filenames.find(filename => filename.includes('./index.'))

  if (indexFilename) {
    storeData = getModule(indexFilename)
  }

  // If store is not an exported method = modules store
  if (typeof storeData !== 'function') {
    // Store modules
    if (!storeData.modules || module.hot) {
      storeData.modules = {}
    }

    for (const filename of filenames) {
      let name = filename.replace(/^\.\//, '').replace(/\.(<%= extensions %>)$/, '')
      if (name === 'index') continue

      const namePath = name.split(/\//)

      name = namePath[namePath.length - 1]
      if (['state', 'getters', 'actions', 'mutations'].includes(name)) {
        const module = getModuleNamespace(storeData, namePath, true)
        appendModule(module, filename, name)
        continue
      }

      // If file is foo/index.js, it should be saved as foo
      const isIndex = (name === 'index')
      if (isIndex) {
        namePath.pop()
      }

      const module = getModuleNamespace(storeData, namePath)
      const fileModule = getModule(filename)

      name = namePath.pop()
      module[name] = module[name] || {}

      // if file is foo.js, existing properties take priority
      // because it's the least specific case
      if (!isIndex) {
        module[name] = Object.assign({}, fileModule, module[name])
        module[name].namespaced = true
        continue
      }

      // if file is foo/index.js we want to overwrite properties from foo.js
      // but not from appended mods like foo/actions.js
      const appendedMods = {}
      if (module[name].appends) {
        appendedMods.appends = module[name].appends
        for (const append of module[name].appends) {
          appendedMods[append] = module[name][append]
        }
      }

      module[name] = Object.assign({}, module[name], fileModule, appendedMods)
      module[name].namespaced = true
    }
    // If the environment supports hot reloading...
    <% if (isDev) { %>
    if (process.client && module.hot) {
      // Whenever any Vuex module is updated...
      module.hot.accept(files.id, () => {
        // Update `root.modules` with the latest definitions.
        updateModules()
        // Trigger a hot update in the store.
        window.<%= globals.nuxt %>.$store.hotUpdate({ modules: storeData.modules })
      })
    }<% } %>
  }
}()

// createStore
export const createStore = storeData instanceof Function ? storeData : () => {
  return new Vuex.Store(Object.assign({
    strict: (process.env.NODE_ENV !== 'production')
  }, storeData, {
    state: storeData.state instanceof Function ? storeData.state() : {}
  }))
}

// Dynamically require module
function getModule(filename) {
  const file = files(filename)
  const module = file.default || file
  if (module.commit) {
    throw new Error('[nuxt] <%= dir.store %>/' + filename.replace('./', '') + ' should export a method which returns a Vuex instance.')
  }
  if (module.state && typeof module.state !== 'function') {
    throw new Error('[nuxt] state should be a function in <%= dir.store %>/' + filename.replace('./', ''))
  }
  return module
}

function getModuleNamespace(storeData, namePath, forAppend = false) {
  if (namePath.length === 1) {
    if (forAppend) {
      return storeData
    }
    return storeData.modules
  }
  const namespace = namePath.shift()
  storeData.modules[namespace] = storeData.modules[namespace] || {}
  storeData.modules[namespace].namespaced = true
  storeData.modules[namespace].modules = storeData.modules[namespace].modules || {}
  return getModuleNamespace(storeData.modules[namespace], namePath, forAppend)
}

function appendModule(module, filename, name) {
  const file = files(filename)
  module.appends = module.appends || []
  module.appends.push(name)
  module[name] = file.default || file
}