#クラシックモード

store/index.js

import Vuex from "vuex"

const createStore = () => {
  return new Vuex.Store({
    state() {
      return {
        count: 0
      };
    },
    getters: {
      getCount: state => state.count
    },
    mutations: {
      incrementCountMutations(state) {
        state.count++;
      }
    },
    actions: {
      incrementCountActions({ commit }) {
        commit("incrementCountMutations");
      }
    }
  });
};

export default createStore

#モジュールモード

動作条件
・index.jsがstoreオブジェクトをexportしない
・store配下にindex.jsが存在しない

store配下にcounter.jsを作成

store/counter.js

export const state = () => ({
  count: 0
})

export const getters = {
  getCount: state => state.count
}

export const mutations = {
  incrementCountMutations(state) {
    state.count++;
  }
}

export const actions = {
  incrementCountActions({ commit }) {
    commit("incrementCountMutations");
  }
}

呼び出す（counter.jsの場合）

pages/index.vue

<template>
  <div>
    state : {{ $store.state.counter.count }}
    <br>
    getters : {{ $store.getters['counter/getCount'] }}
    <br>
    <button @click="$store.commit('counter/incrementCountMutations')">incrementCountMutations</button>
    <br>
    <button @click="$store.dispatch('counter/incrementCountActions')">incrementCountActions</button>
  </div>
</template>

#ヘルパー関数を使用する

pages/index.vue

<template>
  <div>
    state : {{ count }}
    <br>
    getters : {{ getCount }}
    <br>
    <button @click="incrementCountMutations">incrementCountMutations</button>
    <br>
    <button @click="incrementCountActions">incrementCountActions</button>
  </div>
</template>

<script>
import { mapState, mapGetters, mapMutations, mapActions } from 'vuex'
export default {
  computed: {
    ...mapState('counter', [
      'count'
    ]),
    ...mapGetters('counter', [
      'getCount'
    ])
  },
  methods: {
    ...mapMutations('counter', [
      'incrementCountMutations'
    ]),
    ...mapActions('counter', [
      'incrementCountActions'
    ])
  }
}
</script>