component.vue

<template>
  <div class="cmp" v-if="id">
    {{ id }}
  </div>
</template>

<script>
import {createNamespacedHelpers} from 'vuex';
const { mapActions, mapState } = createNamespacedHelpers(
    "users"
);
export default {
  name: 'cmp',
  mounted () {
    this.getUserById(1).then(() => {
        console.log(this.id);
    })
  },
  methods: {
      ...mapActions(['getUserById'])
  },
  computed: {
      ...mapState(["id"]),
  },
}
</script>

store.js

import Vue from 'vue'
import Vuex from 'vuex'
import userModule from './modules/userModule';

Vue.use(Vuex)

export default new Vuex.Store({
  modules: {
    users: userModule
  }
})

userModule.js

export default {
    namespaced: true,
    state: {
        id: null
    },
    actions: {
        getUserById ({commit}, userId) {
            commit('setUserId', userId);
        }
    },
    mutations: {
        setUserId (state, id) {
            state.id = id;
        }
    }
}